There's not really a good compendium of Animal Companion stats available for this game. Below are their fully researched and compiled in-game stats. I have them listed at three points, level 2 start (all companions begin at 2, even if you're only a level 1), the level 7 size buff, and their maximum level 16 stats (even if you're a straight Druid with boon companion, 16 is the highest they can attain).

A note about attacks.
Some companions, like Boar have the Trip (Bite Attack) ability but no actual bite attack. Consequently, they can't make trip attacks. Likewise, the Bear actually HAS a bite attack, but doesn't have the Trip ability listed, so he can't make trip attacks either. The only companions with both the ability and a bite attack to make use of it are: Dog, Leopard, Monitor Lizard, Wolf.
Animal Companions with a single standard attack like the Boar's gore or the Dog's bite gain additional attacks at Base Attack 6 and 11. Animal companions with multiple starting attacks, like the Bear's two claws, or the Smilodon's 5 attacks do not get more attacks as their Base Attack rises. While it might look like the single attackers are getting more pay-off by the end, they won't actually hit 3 attacks until they're level 15 which means you need to be at least 17.

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BEAR
Level 2 - 11HP - Medium
STR 17, Dex 13, Con 13, Int 2, Wis 13, Cha 6
Attacks: 2 Claws +4/4 (BAB 1 + STR 3) and Bite +4
Damage: Claw 1d4+3, Bite 1d6+3
AC: 18 (10 + Dex 1 + Nat 6 + Dodge 1)
Skills: Perception +6
Abilities: Trip Defense +4, Dodge
Speed: 40

Level 7 - 81HP - Large
STR 27, Dex 17, Con 23, Int 2, Wis 13, Cha 6
Attacks: 2 Claws +13/13 (BAB 5 + STR 8 + Enhanced Attacks 2 + Weapon Focus (Claw) 1 - Power Attack 2 - Size 1) and Bite +12 (BAB 5 + STR 8 + Enhanced Attacks 2 - Power Attack 2 - Size 1)
Damage: Claw 1d6+14, Bite 1d8+14
AC: 29 (10 + Dex 3 + Nat 6 + Dodge 1 + Tough Skin 6 + Nat 4 - Size 1)
Skills: Perception +11
Abilities: Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x2, Physical Prowess x3, Tough Skin x2, Toughness, Devotion, Weapon Focus (Claw)
Speed: 40

Level 16 - 248HP - Large
STR 35, Dex 25, Con 31, Int 2, Wis 13, Cha 6
Attacks: 2 Claws +25/25 (BAB 12 + STR 12 + Enhanced Attacks 5 + Weapon Focus (Claw) 1 - Power Attack 4 - Size 1) and Bite +25 (BAB 12 + STR 12 + Enhanced Attacks 5 - Power Attack 4 - Size 1)
Damage: Claw 1d6+25, Bite 1d8+25
AC: 48 (10 + Dex 7 + Nat 6 + Dodge 1 + Tough Skin 21 + Nat 4 - Size 1)
Skills: Perception +20
Abilities: Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x5, Physical Prowess x7, Tough Skin x7, Toughness, Devotion, Weapon Focus (Claw), Improved Evasion
Speed: 40

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BOAR
Level 2 - 13HP - Medium
STR 13, Dex 12, Con 15, Int 2, Wis 13, Cha 4
Attacks: Gore +2 (BAB 1 + STR 1)
Damage: Claw 1d6+1
AC: 21 (10 + Dex 1 + Nat 9 + Dodge 1)
Skills: Perception +6
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge
Speed: 40

Level 7 - 88HP - Large
STR 27, Dex 16, Con 25, Int 2, Wis 13, Cha 4
Attacks: Gore +13 (BAB 5 + STR 8 + Enhanced Attacks 2 + Weapon Focus (Gore) 1 - Power Attack 2 - Size 1)
Damage: Gore 1d8+18
AC: 30 (10 + Dex 3 + Nat 9 + Tough Skin 6 + Dodge 1 + Nat 2 - Size 1)
Skills: Perception +11
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x2, Physical Prowess x3, Tough Skin x2, Toughness, Devotion, Weapon Focus (Gore)
Speed: 40

Level 16 - 264HP - Large
STR 35, Dex 24, Con 33, Int 2, Wis 13, Cha 4
Attacks: Gore +25/20/15 (BAB 12 + STR 12 + Enhanced Attacks 5 + Weapon Focus (Gore) 1 - Power Attack 2)
Damage: Gore 1d8+31
AC: 49 (10 + Dex 7 + Nat 9 + Tough Skin 21 + Dodge 1 + Nat 2 - Size 1)
Skills: Perception +20
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x5, Physical Prowess x7, Tough Skin x7, Toughness, Devotion, Weapon Focus (Gore), Improved Evasion
Speed: 40

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DOG
Level 2 - 13HP - Medium
STR 15, Dex 13, Con 15, Int 2, Wis 12, Cha 6
Attacks: Bite +3 (BAB 1 + STR 2)
Damage: Bite 1d6+3 and Trip
AC: 18 (10 + Dex 1 + Nat 6 + Dodge 1)
Skills: Perception +6
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge
Speed: 40

Level 7 - 88HP - Large
STR 29, Dex 17, Con 25, Int 2, Wis 12, Cha 6
Attacks: Bite +14 (BAB 5 + STR 9 + Enhanced Attacks 2 + Weapon Focus (Bite) 1 - Power Attack 2 - Size 1)
Damage: Bite 1d8+19 and Trip
AC: 27 (10 + Dex 3 + Nat 6 + Tough Skin 6 + Dodge 1 + Nat 2 - Size 1)
Skills: Perception +11
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x2, Physical Prowess x3, Tough Skin x2, Toughness, Devotion, Weapon Focus (Bite)
Speed: 40

Level 16 - 264HP - Large
STR 37, Dex 25, Con 33, Int 2, Wis 12, Cha 6
Attacks: Bite +26/21/16 (BAB 12 + STR 13 + Enhanced Attacks 5 + Weapon Focus (Bite) 1 - Power Attack 2)
Damage: Bite 1d8+32 and Trip
AC: 46 (10 + Dex 7 + Nat 6 + Tough Skin 21 + Dodge 1 + Nat 2 - Size 1)
Skills: Perception +20
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x5, Physical Prowess x7, Tough Skin x7, Toughness, Devotion, Weapon Focus (Bite), Improved Evasion
Speed: 40

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ELK
Note: The Hoof attacks don't show on the Elk's character sheet, but are there when making full attacks.
Level 2 - 13HP - Medium
STR 12, Dex 17, Con 14, Int 2, Wis 15, Cha 5
Attacks: Gore +2 (BAB 1 + STR 1) and 2 Hooves +2/2 (BAB 1 + STR +1)
Damage: Gore 1d8+1, Hoof 1d4+1
AC: 20 (10 + Dex 3 + Nat 6 + Dodge 1)
Skills: Perception +7
Abilities: Trip Defense +4, Dodge
Speed: 50

Level 7 - 88HP - Large
STR 26, Dex 21, Con 24, Int 2, Wis 15, Cha 5
Attacks: Gore +13 (BAB 5 + STR 8 + Enhanced Attacks 2 + Weapon Focus (Gore) 1 - Power Attack 2 - Size 1) and 2 Hooves +12/12 (BAB 5 + STR 8 + Enhanced Attacks 2 - Power Attack 2 - Size 1)
Damage: Gore 2d6+18, Hoof 1d6+13
AC: 29 (10 + Dex 5 + Nat 6 + Tough Skin 6 + Dodge 1 + Nat 2 - Size 1)
Skills: Perception +12
Abilities: Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x2, Physical Prowess x3, Tough Skin x2, Toughness, Devotion, Weapon Focus (Gore)
Speed: 50

Level 16 - 264HP - Large
STR 34, Dex 29, Con 32, Int 2, Wis 15, Cha 5
Attacks: Gore +25 (BAB 12 + STR 12 + Enhanced Attacks 5 + Weapon Focus (Gore) 1 - Power Attack 4 - Size 1) and 2 Hooves +24/24 (BAB 12 + STR 12 + Enhanced Attacks 5 - Power Attack 4 - Size 1)
Damage: Gore 2d6+31, Hoof 1d6+25
AC: 48 (10 + Dex 9 + Nat 6 + Tough Skin 21 + Dodge 1 + Nat 2 - Size 1)
Skills: Perception +21
Abilities: Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x5, Physical Prowess x7, Tough Skin x7, Toughness, Devotion, Weapon Focus (Gore), Improved Evasion
Speed: 50

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GIANT CENTIPEDE
Notes: Poison DC is 10 + Con Mod + 1/2 HD (rounded down)
Level 2 - 11HP - Medium
STR 9, Dex 13, Con 13, Int -, Wis 13, Cha 6
Attacks: Bite +0 (BAB 1 - STR 1)
Damage: Bite 1d6-1 and Poison (DC 12)
AC: 18 (10 + Dex 1 + Nat 6 + Dodge 1)
Skills: Perception +6
Abilities: Immune to Trip, Dodge
Speed: 40

Level 7 - 81HP - Large
STR 23, Dex 17, Con 23, Int -, Wis 13, Cha 6
Attacks: Bite +11 (BAB 5 + STR 6 + Enhanced Attacks 2 + Weapon Focus (Bite) 1 - Power Attack 2 - Size 1)
Damage: Bite 1d8+15 and Poison (DC 20)
AC: 27 (10 + Dex 3 + Nat 6 + Tough Skin 6 + Dodge 1 + Nat 2 - Size 1)
Skills: Perception +11
Abilities: Immune to Trip, Dodge, Power Attack, Evasion, Enhanced Attacks x2, Physical Prowess x3, Tough Skin x2, Toughness, Devotion, Weapon Focus (Bite)
Speed: 40

Level 16 - 248HP - Large
STR 31, Dex 25, Con 31, Int -, Wis 13, Cha 6
Attacks: Bite +23/18/13 (BAB 12 + STR 10 + Enhanced Attacks 5 + Weapon Focus (Bite) 1 - Power Attack 4 - Size 1)
Damage: Bite 1d8+28 and Poison (DC 28)
AC: 46 (10 + Dex 7 + Nat 6 + Tough Skin 21 + Dodge 1 + Nat 2 - Size 1)
Skills: Perception +20
Abilities: Immune to Trip, Dodge, Power Attack, Evasion, Enhanced Attacks x5, Physical Prowess x7, Tough Skin x7, Toughness, Devotion, Weapon Focus (Bite), Improved Evasion
Speed: 40

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LEOPARD
Note: Size Increase actually occurs at 4th level, but still doing comparison at 7th.
Level 2 - 11HP - Small
STR 12, Dex 21, Con 13, Int 2, Wis 12, Cha 6
Attacks: Bite +7 (BAB 1 + DEX 5 + Size 1) and 2 Claws +7/7 (BAB 1 + DEX 5 + Size 1)
Damage: Bite 1d4+1 and Trip, Claw 1d3+1
AC: 20 (10 + Dex 5 + Nat 4 + Size 1)
Skills: Perception +6
Abilities: Trip (Bite Attack), Trip Defense +4, Weapon Finesse
Speed: 50

Level 7 - 81HP - Medium
STR 22, Dex 25, Con 23, Int 2, Wis 12, Cha 6
Attacks: Bite +12 (BAB 5 + DEX 7 + Enhanced Attacks 2 - Power Attack 2) and 2 Claws +12/12 (BAB 5 + DEX 7 + Enhanced Attacks 2 - Power Attack 2)
Damage: Bite 1d6+13 and Trip, Claw 1d4+13
AC: 30 (10 + Dex 7 + Nat 2 + Nat 4 + Tough Skin 6 + Dodge 1)
Skills: Perception +11
Abilities: Trip (Bite Attack), Trip Defense +4, Weapon Finesse, Dodge, Power Attack, Evasion, Enhanced Attacks x2, Physical Prowess x3, Tough Skin x2, Toughness, Devotion
Speed: 50

Level 16 - 248HP - Medium
STR 30, Dex 33, Con 31, Int 2, Wis 12, Cha 6
Attacks: Bite +24 (BAB 12 + DEX 11 + Enhanced Attacks 5 - Power Attack 4) and 2 Claws +25/25 (BAB 12 + DEX 11 + Enhanced Attacks 5 + Weapon Focus (Claw) 1 - Power Attack 4)
Damage: Bite 1d6+24 and Trip, Claw 1d4+24
AC: 49 (10 + Dex 11 + Nat 2 + Nat 4 + Tough Skin 21 + Dodge 1)
Skills: Perception +20
Abilities: Trip (Bite Attack), Trip Defense +4, Weapon Finesse, Dodge, Power Attack, Evasion, Enhanced Attacks x5, Physical Prowess x7, Tough Skin x7, Toughness, Devotion, Weapon Focus (Claw), Improved Evasion
Speed: 50

MASTODON
Note: Overrun works on non-hostile NPCs too. It's unbelievably fun to send your Mammoth charging around the throne room or the city square knocking all the NPCs down everywhere.
Level 2 - 11HP - Medium
STR 14, Dex 14, Con 13, Int 2, Wis 13, Cha 7
Attacks: Gore +3 (BAB 1 + STR 2) and Slam +3 (BAB 1 + STR 2)
Damage: Gore 1d8+2, Slam 1d6+2
AC: 20 (10 + Dex 2 + Nat 7 + Dodge 1)
Skills: Perception +6
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge
Speed: 40

Level 7 - 81HP - Large
STR 28, Dex 18, Con 23, Int 2, Wis 13, Cha 7
Attacks: Gore +14 (BAB 5 + STR 9 + Enhanced Attacks 2 + Weapon Focus (Gore) 1 - Power Attack 2 - Size 1) and Slam +13 (BAB 5 + STR 9 + Enhanced Attacks +2 - Power Attack 2 - Size 1)
Damage: Gore 2d6+15, Slam 1d8+15
AC: 30 (10 + Dex 4 + Nat 7 + Nat 3 + Tough Skin 6 + Dodge 1 - Size 1)
Skills: Perception +11
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge, Overrun, Power Attack, Evasion, Enhanced Attacks x2, Physical Prowess x3, Tough Skin x2, Toughness, Devotion, Weapon Focus (Gore)
Speed: 40

Level 16 - 248HP - Large
STR 36, Dex 26, Con 31, Int 2, Wis 13, Cha 7
Attacks: Gore +26 (BAB 12 + STR 13 + Enhanced Attacks 5 + Weapon Focus (Gore) 1 - Power Attack 4 - Size 1) and Slam +25 (BAB 12 + STR 13 + Enhanced Attacks +5 - Power Attack 4 - Size 1)
Damage: Gore 2d6+26, Slam 1d8+26
AC: 49 (10 + Dex 8 + Nat 7 + Nat 3 + Tough Skin 21 + Dodge 1 - Size 1)
Skills: Perception +20
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge, Overrun, Power Attack, Evasion, Enhanced Attacks x5, Physical Prowess x7, Tough Skin x7, Toughness, Devotion, Weapon Focus (Gore), Improved Evasion
Speed: 40

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MONITOR LIZARD
Notes: Poison DC is 10 + Con Mod + 1/2 HD (rounded down)
Level 2 - 11HP - Medium
STR 13, Dex 17, Con 12, Int 2, Wis 12, Cha 6
Attacks: Bite +2 (BAB 1 + STR 1)
Damage: Bite 1d6+1 and Trip
AC: 18 (10 + Dex 3 + Nat 4 + Dodge 1)
Skills: Perception +6
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge
Speed: 30

Level 7 - 81HP - Large
STR 27, Dex 21, Con 22, Int 2, Wis 12, Cha 6
Attacks: Bite +13 (BAB 5 + STR 8 + Enhanced Attacks 2 + Weapon Focus (Bite) 1 - Power Attack 2 - Size 1)
Damage: Bite 1d8+18 and Trip and Poison (DC 19)
AC: 27 (10 + Dex 5 + Nat 4 + Nat 2 + Tough Skin 6 + Dodge 1 - Size 1)
Skills: Perception +11
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x2, Physical Prowess x3, Tough Skin x2, Toughness, Devotion, Weapon Focus (Bite), Monitor Lizard's Venom
Speed: 30

Level 16 - 248HP - Large
STR 35, Dex 29, Con 30, Int 2, Wis 12, Cha 6
Attacks: Bite +25/20/15 (BAB 12 + STR 12 + Enhanced Attacks 5 + Weapon Focus (Bite) 1 - Power Attack 4 - Size 1)
Damage: Bite 1d8+31 and Trip and Poison (DC 28)
AC: 46 (10 + Dex 9 + Nat 4 + Nat 2 + Tough Skin 21 + Dodge 1 - Size 1)
Skills: Perception +20
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x5, Physical Prowess x7, Tough Skin x7, Toughness, Devotion, Weapon Focus (Bite), Monitor Lizard's Venom, Improved Evasion
Speed: 30

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SMILODON
Level 2 - 11HP - Medium
STR 13, Dex 17, Con 13, Int 2, Wis 15, Cha 10
Attacks: Bite +2 (BAB 1 + STR 1) and 4 Claws +2/2/2/2 (BAB 1 + STR 1)
Damage: Bite 1d6+1, Claw 1d4+1
AC: 18 (10 + Dex 3 + Nat 4 + Dodge 1)
Skills: Perception +7
Abilities: Trip Defense +4, Dodge
Speed: 40

Level 7 - 81HP - Large
STR 27, Dex 21, Con 23, Int 2, Wis 15, Cha 10
Attacks: Bite +12 (BAB 5 + STR 8 + Enhanced Attacks 2 - Power Attack 2 - Size 1) and 4 Claws +13/13/13/13 (BAB 5 + STR 8 + Enhanced Attacks 2 + Weapon Focus (Claw) 1 - Power Attack 2 - Size 1)
Damage: Bite 1d8+14, Claw 1d6+14
AC: 27 (10 + Dex 5 + Nat 4 + Nat 2 + Tough Skin 6 + Dodge 1 - Size 1)
Skills: Perception +12
Abilities: Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x2, Physical Prowess x3, Tough Skin x2, Toughness, Devotion, Weapon Focus (Claw)
Speed: 40

Level 16 - 248HP - Large
STR 35, Dex 29, Con 31, Int 2, Wis 15, Cha 10
Attacks: Bite +24 (BAB 12 + STR 12 + Enhanced Attacks 5 - Power Attack 4 - Size 1) and 4 Claws +25/25/25/25 (BAB 12 + STR 12 + Enhanced Attacks 5 + Weapon Focus (Claw) 1 - Power Attack 4 - Size 1)
Damage: Bite 1d8+25, Claw 1d6+25
AC: 46 (10 + Dex 9 + Nat 4 + Nat 2 + Tough Skin 21 + Dodge 1 - Size 1)
Skills: Perception +21
Abilities: Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x5, Physical Prowess x7, Tough Skin x7, Toughness, Devotion, Weapon Focus (Bite), Improved Evasion
Speed: 40

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WOLF
Level 2 - 13HP - Medium
STR 13, Dex 15, Con 15, Int 2, Wis 12, Cha 6
Attacks: Bite +2 (BAB 1 + STR 1)
Damage: Bite 1d6+1
AC: 18 (10 + Dex 2 + Nat 5 + Dodge 1)
Skills: Perception +6
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge
Speed: 50

Level 7 - 88HP - Large
STR 27, Dex 19, Con 25, Int 2, Wis 12, Cha 6
Attacks: Bite +13 (BAB 5 + STR 8 + Enhanced Attacks 2 + Weapon Focus (Bite) 1 - Power Attack 2 - Size 1)
Damage: Bite 1d8+18
AC: 27 (10 + Dex 4 + Nat 5 + Nat 2 + Tough Skin 6 + Dodge 1 - Size 1)
Skills: Perception +11
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x2, Physical Prowess x3, Tough Skin x2, Toughness, Devotion, Weapon Focus (Bite)
Speed: 50

Level 16 - 264HP - Large
STR 35, Dex 27, Con 33, Int 2, Wis 12, Cha 6
Attacks: Bite +25/20/15 (BAB 12 + STR 12 + Enhanced Attacks 5 + Weapon Focus (Bite) 1 - Power Attack 2)
Damage: Bite 1d8+31 and Trip
AC: 46 (10 + Dex 8 + Nat 5 + Tough Skin 21 + Dodge 1 + Nat 2 - Size 1)
Skills: Perception +20
Abilities: Trip (Bite Attack), Trip Defense +4, Dodge, Power Attack, Evasion, Enhanced Attacks x5, Physical Prowess x7, Tough Skin x7, Toughness, Devotion, Weapon Focus (Bite), Improved Evasion
Speed: 50

is taking infusion on an alchemist (like Jubilost) to infuse transformation spell onto animal companions a good combo?

Yes, actually, it's a fantastic combo. The spell scales off the person casting it, not the target. So interestingly, let's say you have one level of Druid and a starting Dog companion, right? Then a 20th level Alchemist casts Transformation on the Animal Companion, it now has a Base Attack of +20, four attacks a round, along with all the AC and attribute upgrades.

Here are some thoughts about the various animal companions. I generally think of the animals in sort of subgroups.

SINGLE ATTACK TRIPPERS
Functionally, the Dog, Wolf and Monitor Lizard are all pretty much the same. Their AC, attacks and damage are all within a single point of one another, and they all trip with their primary attack.

Dog: 88HP, AC 27, Atk +14, Dmg 1d8+19, Speed 40
Lizard: 81HP, AC 27, Atk +13, Dmg 1d8+18, Speed 30
Wolf: 88HP, AC 27, Atk +13, Dmg 1d8+18, Speed 50

Most of the time, speed is going to be irrelevant. And while the Monitor Lizard looks like its at a disadvantage because of the lagging HP, the fact that it's the only one of the three with built-in venom that discharges every bite, it's actually the strongest of the three. In most cases, there's never a time where you'd want a Dog or a Wolf over a Monitor (unless for RP purposes).

MULTI-ATTACKERS*
There are some companions who basically just have the ability to attack more than once and nothing else special about them. The Bear, Elk and Smilodon fill these ranks. Granted, the Smilodon has an unlisted pounce ability, but most of the time your pets are just going to be auto-attacking at your frontlines.

Bear: 81HP, AC 29, Atks +13*2/+12, Dmg 2d6+1d8+42 (45-62)
Elk: 88HP, AC 29, Atks +13/+12*2, Dmg 4d6+44 (48-68)
Smilodon: 81HP, AC 27, Atks +12/+13*4, Dmg 5d6+1d8+70 (76-108)

Obviously the Smilodon is far and away the strongest companion in this category and arguably strongest overall. Five attacks are nonsense, especially if you're a class that can squeeze Teamwork feats on it like Precise Strike, functionally turning them all into Sneak Attacks. What's interesting though is the disparity between the Bear and Elk. The Elk appears to be a straight upgrade, same AC, higher damage, better HP. There's a unique weapon out there that will upgrade the bear's attacks to deal an additional +2d10 elemental damage per hit, and even though it would similarly upgrades the Elk's attacks by +2d6, the Bear pulls ahead. In most cases (outside using that bear-enhancing scimitar), there's never a time where you'd want a Bear over an Elk, and never either over a Smilodon (unless you despise the Sabercats like I do for being so damned broken.)

SPECIAL POWERED COMPANIONS
This group doesn't directly compete with one another, but rather have unique abilities that make them stand out alone in the animal companion groups.

Boar: Ferocity (continues fighting at 0HP until death)
Giant Centipede: Venom (Dex Damage)
Leopard: Trip AND Multiattack
Mastodon: Overrun (Massive AoE Trip)

Boar: Normally, I hate Ferocity. Anyone that plays with Regongar knows that it makes him die constantly. Usually enemies will stop targeting your party when they drop unconscious, and since Ferocity characters don't, they tend to be targeted until they die. What a goddamn pain. But your Boar dying is no big deal, he resurrects after every rest, so the ability has some merit. Still, it's not that great and probably the worst of the Special Powered Companions.

Giant Centipede: The Centipede is basically a downgrade of the Monitor Lizard. They both have Venom of comparable strength, but it has a weaker bite damage, lower attack and no Trip ability. Fun for RP purposes, but there's not really a situation where the Centipede is ever better than the Monitor.

Leopard: The Leopard is generally perceived to be nearly as overpowered as the Smilodon and as such is probably the second most selected companion. I find most of its reputation is undeserved. Sure, it has pounce like the Smilodon, but as I mentioned on its article, that only comes up so many times a fight. The innate three attacks are nice, though single attackers ultimately reach the same number - often even surpassing if they're met with a Transformation spell (putting them at 4 attacks). But the Leopard's Trip attack lags behind his fellows. See, Trip gets a bonus from size and the Leopard is the only small/medium companion in the game, making its Trip the weakest. And then its three attacks are actually weaker than most other multiattackers like the Elk.

Mastodon: The Mastodon is quite possibly the most useful companion of them all, Smilodon included. When it achieves its size upgrade, it gains the ability to charge across the battlefield tripping everything in its way. With spells and items you can boost this ability (which already has a very high check). And the ability is spammable. It's not inconceivable to keep an entire field of enemies locked down with a single Mastodon charging back and forth. God help an enemy group if you happen to have TWO or more of these guys!

RESULTS
The three best Companions then (in my estimation) are:

1. Mastodon
2. Smilodon
3. Monitor Lizard

*Updated with correct information from happygui

Bear has 3 attacks per round, 2 claws + 1 bite.

Boar and Mastodon can trip with bite if we turn them into something can bite by spells, although they’ll lost 1 AB because their Weapon Focus is gore.

Right now (2.1.5d) Boar, Dog, Giant Centipede, Monitor Lizard and Wolf still have attacks stacking bug, so in late game when every animal becomes smilodon, they’ll have 4~6 more attacks per round than others.

I’m not sure this is bug or something, when hire a mercenary with animal companion, and max out their level before they join in, the animal will have 4 more feats than usual.

Regular version
https://i.imgur.com/6m2Zu6A.jpg

4 more feats version
https://i.imgur.com/xtacuMK.jpg

You're right about the Bear bite. It's an unlisted bite attack, but I wonder how I missed that in my testing?

As far as the polymorph for bite attacks, that's why I included the blurb that they have the feat but no access to the attack in the OP.

And the extra feats are how it's SUPPOSED to work but there's a bug where after level 11 the companion just stops getting new feats and their slots are filled with the same version of Weapon Focus over and over. I didn't know that merc pets were functioning correctly (I avoid using mercs, personally).

Thanks for the info!

I feel you negleted the main reason why people value the Leopard so much: Because it doesn't become large. Most of the game you spend fighting in tight corridors/tunnels so having large pets to manouver around becomes a pain and they obstruct your frontline, or just end up getting killed. Anyway, that's the main reason I value the Leopard over the others.

I was wondering about one thing about bear not getting trip attacks. What if player character is Mad Dog, and he gets ferocious fetch feat, which gives improved trip to all (I guess) his pets. And since bear has bite attacks, would that feat allow it to trip enemies? Or it wouldn't work because bear doesn't have "basic" trip in the first place?

Wait. Do animal companions actually fight when taken by classes other than the kineticist?

You're talking about familiars (pets). They don't fight, just give passive boosts to stats and/or skillchecks. This topis is about animal companions that quite a few classes get. They fight like any other party member.