1. Half-Giant Fighter/Psionicist
Serves as the party healer with Lend Health and Cell Adjustment, as well as a strong physical attacker. The logic behind using one as healer is that Lend Health looks like it's stronger than divine healing, while high HP, regen from high CON, and Cell Adjustment compensates for the downsides. Later Psi choices geared toward making her a better fighter offensively and defensively.
(Strictly speaking, might replace Fighter with Ranger (Earth) for very limited magic ability.)

2. Thri-kreen Fighter/Druid (Fire)/Psionicist
Another fighter, this time taking advantage of the thri-kreen's unique traits. Psionics can compensate for poor defense and other thri-kreen limitations and may allow dominate effects later. Also, Enhanced Strength gives 24 strength. Fire gives her Flame Blade and some other useful spells. At higher levels, can help with healing.

3. Halfling Druid (Earth)/Psionicist
Primary divine caster. Earth gives her an attack spell right away and Ironskins later. High Wisdom allows for high chance of Mass Dominate/Disintegrate, as well as more PP and spell slots. Secondary healer, perhaps transitioning to primary later (but poor HP makes Lend Health less attractive here).

4. Half-Elf Fighter/Preserver/Thief (Telepathy)
Fills the thief role, as well as being the party's arcane caster (and hence being particularly useful against larger groups of spellcasters). Telepathy provides Superior Invisibility, which is Int based (although I am not sure if it is really that great) as well as Psionic Blast and Ego Whip.

How does this party look?

Earth and Fire druids? I guess they have the good elementals, but I always considered a water druid almost obligatory. I just assumed there were likely to be plot elements accessible only if you have access to the water sphere. I don't think that's actually the case, but I just felt that with the desert setting water worship is too likely a plot element for me to ignore and it became narratively required in my mind.

Why halfling on the earth druid/psionicist? Just for the sake of party diversity? Maybe something beefier? I know Muls can't druid/psion but can't Half-Giants? I'd even take human over halfling.

I prefer to play with four fighters (or rangers), two preservers, two druids, at least one psionicist, and one thief. A good starter party is a half-elf fighter/druid (fire)/preserver, elf fighter/preserver/thief, thri-kreen fighter/druid (earth)/psionicist, and half-giant fighter/psionicist. The most important thing is that they can all buff themselves and fight. Buffed and at full-strength, they're unstoppable until the final battle. With two preservers and two druids, you can easily keep them healed and buffed between rests. Otherwise, you'll run out essential spells, such as haste or fireball.

Another fun one is a half-giant fighter/cleric (fire), half-giant fighter/psionicist, elf fighter/preserver/thief, and half-elf fighter/druid (earth)/preserver. Use the half-giants as shock troops. The elves can caste haste and soften up the enemies with fireballs. This party is stronger on melee but weaker on healing. It's not a big deal. Its unlikely anything can defeat two hasted half-giants, and they'll drag the unconscious elves to the next rest point if necessary. Still, don't get too cocky. High AC giants and low hp elves are poor on defense.

Don't bother to maximize your characters' attributes. It's more important to use a proper strategy. Experiment with spells, but my favorites are haste and fireball. Everything beyond that is just gravy. Blink, blur, mirror image, fire shield, minor globe of invulnerability, and stoneskin help a lot. This is why you want two preservers, not just one. You can probably win the game with any party, but two triple-classed preservers makes it much easier in my experience.

There aren't enough Water spells for it to be a useful choice, and of those that exist, one of them is a worse Cause Serious Wounds, and one has a worse Cure Serious Wounds as one of its two possible effects.

Halflings can get 22 Wisdom. This means:
At Druid level 9, 3 5th level spells per day
More power points per level
Better psionic power scores. Mass Dominate gets 16 at the start, leading to an 80% success rate (before checking enemy defenses)

Half-Giants can't be Druids. Clerics are not a good alternative because they don't get 4th or 5th level healing spells, leaving them only with the pathetically weak Cure Light wounds for healing (and possibly Aid depending on how temporary hit points actually work, but that doesn't heal any more).

@dtgreene
Wisdom is a major driver for psionic strength points (psp's), so I don't consider a half-giant to be worthwhile as a psionicist. But, I'll try the half-giant you mentioned to see how well it works in practice.

You're right that halflings are great for any Wisdom-based class since they max out at 22.

Single class is very desirable since it takes a lot less time to level up. Your warriors' hit points also get diluted by the other class. That said, there's no shortage of experience in this game, so all multi-class can be fun if not maximal.

Likewise, your preserver will take forever to get his powerful spells due to the triple class. Preservers are great at crowd control, and some of the better AoE's are in the 4th and 5th levels of spells. So I'd cut a class there.

Also, don't overrate healing. Mid-combat healing is usually worse than just kill-kill-kill, and even clerics can cast 5-6 Cure Light Wounds and 4-5 Aid by level 5 depending on their Wisdom. 9d8 averages out to 40.5 hit points of healing between combat, which often does enough to get to the next rest area.

40.5 isn't enough to heal one character to full, let alone healing the party, and my understanding is that rest spots might not always be available or convenient.

The thing with half-giant psionicists is that they have a lot of hit points, and that HP can be used for burst healing with Lend Health, which is capable of healing more with a single action than any healing spell. Also, Lend Health only costs 4 PSPs. In fact, none of the Psychometabolic powers are particularly expensive except Enhanced Strength, and that power's initial cost is 0 if you have 24 Strength. (You can then use Share Strength and still have 24 Strength; the only problem then becomes the total maintenance cost of 10/round.)

By the way, in the sequel, the combination of Heal and Lend Health looks like it could be quite powerful. Have your Half-Giant Fighter/Psionicist use Lend Health to heal the rest of the party, and then cast Heal on the Half-Giant to regain all of the health that had been lent. Heals your entire party by a substantial amount for only 12 PSPs and one 6th level spell.

I still haven't started the first game, but I am already thinking about my party for the second game. I think it might be something like this:

Half-Giant Gladiator (Metabolism): High HP, powerful fighter. No longer a psionicist, but that means more HP, and *Lend Health is usable by non-psionicists* this time around. That's a lot of HP (182 max at the start) to lend to allies.

Thri-kreen Fighter/Druid/Psionicist: As above. Might be my only long-term psionicist.

Human Gladiator 7->?->Druid (Earth): Here we go with dual-classing. The reasoning behind the dual-class is to get Heal sooner. ? can be either Thief or Psionicist.

Human Gladiator 7->?->Preserver. Get the good spells sooner, since the level cap is higher, allowing more powerful spells to exist.

One thing might change my plans: Is there a way to get Wisdom up to 24 (for the 6th level bonus spells) in the second game? (This would be really nice for the bonus 6th level Druid spells and hence extra casts of Heal.)

Lend Health as a wild talent is much more enticing since you don't have to dilute your character. Definitely something I overlooked in my playthroughs, though I prefer to transfer my party.

Dual class is also quite powerful. My mage is a Preserver/Cleric/Psionicist at levels 9/5/5 going into Ravager, so he kinda got the best or at least better of a bunch of worlds. Gladiator's also a great choice for HP and beatdown utility.

I can't recall any spots where that much Wisdom could be acquired, or even any ability score adjustments FWIW. I actually think there's more ability score adjustments in SL, however, I only beat Ravager once (doing most of the side quests) so take that as you will.

You could opt for a mix: Transfer 3 of your characters and fill the 4th slot with the half-giant from the default Ravager party (who has 165 HP and max physical stats). This way you can keep 75% of your previous party and still have a high HP character with Lend Health.

The reason I ask about high Wisdom is that I don't consider 5th level spells that important when the spell I am most interested in having more casts of, Heal, is 6th level. According to the manual, you start getting bonus 6th level spells at 23 Wisdom which is unfortunately 1 more than what a Halfling can start with.

There is the Ring of Insight in Shattered Lands, which grants +2 Wisdom. It will transfer over.

I won't spoil where you get it here though. Guess I should start a magic items spoiler thread.

The problem is that, from what I have read, transferring characters will double the HP of enemies, and I don't want that.

Here's an alternate idea for the humans:

Human Gladiator 7->Preserver 3->Druid 12, then reincarnate. This way I get 2 casts of Heal relatively quickly, and then become a multi-class character and learn Reincarnate (required for the other human's setup to work).

Human Gladiator 7->Thief 5->Preserver 12 (or maybe 13?), then reincarnate. This gets thief skills covered and the Reincarnate spell (to allow the first human's setup to work).

When reincarnating, if a character becomes a thri-kreen, I would either reload or reincarnate again. Otherwise, there isn't much difference (other than the double rolled HP a half-giant gets, but I haven't tested to see if that works for triple-class characters).

Second character could be a Ranger, trading 1 AC for level 1-3 Cleric spells, but I don't know if that's worth it.

The Reincarnate spell is so powerful that it affects the builds of characters who *don't* learn the spell.