Sort of tempted to play Wizardry 8, with a party like the following:
* Dracon Valkyrie
* Mook Ranger (Giant Sword)
* Bard (unsure about race)
* Fairy Mage, replaced later with Gadgeteer (unsure about race)
* Dwarf Bishop, changing to Fighter at level 12 (after learning a portal spell)
* Elf Bishop

How does this sound?

And I still don't know how best to build Gadgeteers, particularly if I'm going to largely ignore the Omnigun. (I don't like the blindness effect.)

I have put some slight fighter prioritization with Priest and Alchemist in the past, and would like to try that with Bishop. One thing is that, while you may only have one attack, having high Strength allows you to get the most of that one attack, and there are some nice weapons usable by many of these classes like The Mauler, Diamond Eyes (if you aren't using it as an off-hand weapon for someone else), and the Staff of Doom (put the Bishop's Artifacts skill bonus to good use in order to Death Cloud enemies before you'd normally get access to that spell).

Going STR/INT allows you to still get Power Cast, or you can go STR/DEX or so to really focus on fighting. Also, you can switch to Fighter or a hybrid once you've learned the most important spells.

By the way, the Valkyrie's Cheat Death ability is great in conjunction with the ability to revive; for that reason, it can be worth putting points into the Valkyrie's Artifacts so that she can equip the Amulet of Life.

Your party is great, having a Valkyrie, Ranger, Bard, Gadgeteer, and two Bishops, one becoming a Fighter. You're like me, wanting to take advantage of all the great instruments and gadgets out there, good magic, and good fighting skills.
Why would you ever go Str/Dex on a caster? They're tier 3 fighters. They will never be as good as even a Bard or Gadgeteer.
My Priest and Alchemist have Intelligence, Piety, Speed, and Senses maxed. They have Strength, Vitality, and Dexterity at 59 and 60 as Humans. I would think that they would do ok in melee combat (honestly, how many times am I going to rely on my Priest and Alchemist for melee damage)? Probably I could count it on one hand.

They'll still be better at casting spells using SP than a Bard or Gadgeteer. This is especially true for important spells you can't stamina cast, like Heal Wounds (at lower levels, before stamina cast Heal All is a thing) and the Portal spells.

Also, you can start as a caster, learn important spells that otherwise might be missing in your party (most notably the long-duration spells), and then change to a fighter or hybrid later, at which point by end-game you may reach or surpass the Bard/Gadgeteer fighting abilities (while having things like a primary bonus to a fighting skill, the option of using fighter-type only weapons (Giant Sword for a Mook Bishop/Fighter, for example), and abilities like Berserk).

(Also, I really think they should have made Priests have the same fighting values as Bard and Gadgeteer; their spells are weaker offensively than the other types, they have more HP than the other casters (and better equipment, except that Bishop has the same equipment options for some reason), and in the early games, gained accuracy at the same rate as Fighters.)

Also, worth noting that Str/Int can still be a good choice, simply because of how substantial the Str bonus to melee damage is.

My Human Bard and Gadgeteer have just unlocked the 3rd attack per round, and have a potential for 3 swings per turn.
This is a potential for 9 melee attacks per round. That could make them godly with Light Swords and Shields.
Also, they have the potential for 3 ranged attacks per turn, with a maximum of 3 swings per attack (+2 from the Tripleshot Crossbow), bringing their total ranged attack potential to 15 attacks per turn.
The Priest and Alchemist, if I focus on melee fighting, will only ever get 2 swings per attack, and 2 attacks per turn, with the Mauler or Diamond Eyes (not both), and the Staff of Doom, respectively.
The Psionic and Mage are useless in melee, at this point, as the Staff of Doom is taken by the Alchemist. They might as well focus on Slings (with the Wrist Rocket and Sling's + to Initiative, 3 swings per attack is possible, provided they aren't encumbered). Two attacks per turn in ranged combat is the best they can hope for.

Those two items are not reliably available, so I do not consider them when planning builds.

Two swings per attack is enough much of the time, just because of how powerful melee combat is relative to missile or magic in this game.

Also, it is worth noting that Diamond Eyes, The Mauler, and the Staff of Doom are, I believe, stronger than any reliably obtainable sword other than the Giant Sword, which is only usable by Mooks, and not by Bards or Gadgeteers.

In all of my other parties, besides this one (MDP), I have always had a Fighter and Rogue present, because I consider melee damage to be so badass.
This particular MDP has the Bard and Gadgeteer as the badasses, so it will probably come as no surprise that I want them, with their mediocre fighting abilities, to be able to dish out the pain in melee. They just gained level 34, which qualifies them for their third attack per round, just like the Fighter and hybrids.
I know that the Bayjin chest is almost impossible to "grind", due to how the game spawns treasures before you first enter an area. The best bet is talking to Jan-Ette 50 times for a Light Shield, and grinding the Buccaneer Ghosts for Light Swords and Light Shields.
Two swings per attack is not guaranteed, but at least one swing per attack will have the potential for KO with maces, or kill with the Staff of Doom.
Unfortunately, with this party (Bard, Gadgeteer, Priest, Alchemist, Psionic, Mage), only one (the Priest) will be able to use any Mace and Flail weapons at all, leaving him with the choice between the Mauler or Diamond Eyes.
The Bard and Gadgeteer will grind for Light Swords and Light Shields, even if it takes a week. The Priest, as said above, will focus on the better Mace and Flail weapon.
This leaves the Alchemist, Psionic, and Mage to fight for the Staff of Doom. The Alchemist is physically the toughest out of the three (best armor and hit points), so why shouldn't he get it? The weak Psionic and Mage can focus on slings.

There are diminishing returns with melee, but physical combat is more or less required, and it's just more fun to not have to rely on summons for that. Now, the total physical damage of a party only really needs to be equivalent to, say, approximately two fighters in melee, but, why not more? Two speed casters are enough, in the same vain, if you're even going for that. A certain someone likes to combine speed casters with slingers, attempting to max intelligence, speed, senses, and dexterity. And, why not? Low piety is good enough, same with vitality. It's maxing the K.O. rolls for when magical damage isn't the answer. Also, specialist casters only really need to pump their book until it hits a natural thirty-six, so might as well pump a combo of close/range combat and a weapon skill.

Swords are, essentially, the one-handed polearms: peaks early, etc. Early mid-game, maces and staves are pretty lackluster, to be honest. Swords and polearms are—one-hundred percent—end-game viable, but so is, even, a punch ninja. Don't get me started on dagger rogues... I'll say it a thousand times if I must: it's an easy game. Nevertheless, optimization is fascinating for its own sake.

For a party, what is comfort? Some say having all four books of magic. Some say as many fighters as possible. I, personally, enjoy having the long-term buffs early, so a mage and priest, or, alternatively, a bishop. Ultimately, it boils down to play style. But, six gishes tends to have a rough early mid-game.

Counter-argument: The Staff of Doom allows for casting Death Cloud, and therefore might be a better choice for a character who lacks that spell, or better lacks good air spells in the first place. Taking this into account:
* Alchemist is the worst choice here because they can cast Death Cloud anyway (not to mention Toxic Cloud).
* Mage has Asphyxiate and Noxious Fumes, so the staff is not that important, though still a better choice than Alchemist in this case.
* Psionic, on the other hand, is rather lacking in Air spells (and in multi-target instant death spells, for that matter). Hence, the Psionic might actually be the best choice from this perspective.

(Note that you can recharge this weapon by selling and buying it back, though you will need to uncurse it first, and this is one of the harder weapons to uncurse. Remember that Remove Curse backfires will trigger an assertion (crash) if the backfire reduces SP below 0.)

Well, there is the Giant's Sword, but you either need to plan to use it at the start, or do a character replace once you discover that only one particular race can equip it.

By the way, for Giant's Sword users, what build do you prefer?

There are some decent mace options, even earlier on.
* Mace: Has a 5% KO chance, which can come in handy if the enemy's level isn't too high (and the enemy isn't immune).
* Bullwhip: Requires a bit of luck to get early, but it's a nice extended range weapon that only uses one hand. Very useful if you want to use a shield, but still want to be able to attack from the back. (In particular, note that Priests and Bishops can equip this, and there are some shields that provide bonuses that are nice to have on a back-row caster.)
* Hammer: Has a 5% KO chance, can be used in the off-hand, and boosts Mace & Flail, improving accuracy with the main-hand mace. It's actually not that easy to come up with a better off-hand weapon, with the only obvious choice using the same skill.
* Stun Mace and Disruptor Mace have really good KO chances.

(Also, there actually isn't anything preventing Priests and Bishops from dual-wielding, although note that the lack of the Dual Wielding skill means they won't be particularly good, unless they've spent time in a different class to build up the skill.)

Note that you can get this with class change or character replacement, using such characters early and then either class changing once you have the spells at a good level or replacing once other characters can cover them. (For example, you might replace your Priest once your Bard and Gadgeteer can cover Magic Screen and Armorplate respectively.)

More theorycrafting: Bishop to Lord

The idea is this:
Race: Dwarf
Class: Bishop. change to Lord at level 9(?)
Stats: STR/SPD until Speed at 50, then perhaps STR/DEX
Skills: Mace & Flail, Wizardry (ideally to 50, Divinity (other spellbooks unimportant). After class change, Dual Wield,
Spells: All the long duration spells, plus important healing spells (including condition cures), with a particular emphasis on spells that might not otherwise be covered. (In particular, try to learn X-Ray at level 8, as you won't be able to later.)

So, as for the explanation:

* Race: Dwarf is chosen as a race for the damage resistance. Bishops have poor HP, and this character is going to be in the front ranks, so having some damage mitigation should help, especially early on. Also, Dwarf stats happen to be in a pretty good position for the class change, the only issue being Speed, which will reach 50 at level 8 (fast enough for our purposes). One could do this with other races, most notable human, but make sure you meet all the stat requirements (notably Vitality might be easy to forget), and you won't have the physical damage resistance a Dwarf gets.

* Class: Lord is chosen because they get Dual Weapons, which happens to work rather well with Mace & Flail, which is already available as a weapon skill for the Bishop, so you do get a head start there. (Also note that, if you have to change back into a Bishop because you forgot a spell you really want, for example, you can still Dual Wield The Mauler + Diamond Eyes as a Bishop, even if you can't improve Dual Weapons any further.)

* The class change level of 9 is chosen so that X-Ray is available to this character; that is a spell that you'll *definitely* want to have available. It may not be enough to reliably cast level 2 Mage spells at PL7, but it's still good enough for non-combat spells. Furthermore, it gives Dual Weapons a chance to grow during the long level of 10. Note that your magic won't improve at all from 9 until 13, and Portal spells still won't be available until level 15. Waiting to 11 for the Portal spells is an option, though it will make the character worse at fighting in the long run, and means you don't get to start raising Dual Wield until later. A level 8 class change keeps you from learning X-Ray, and a change earlier is not actually possible for a Dwarf.

* Stats: Strength has a very noticeable effect on melee damage, so of course we want it high. Speed must be at least 50 to change into a Lord, and neither Dwarf nor Bishop provides it. On the other hand, Bishop does conveniently provide Dexterity and Senses, two stats that can help with physical combat that a Dwarf naturally lacks. (Of course, you still pay with starting bonus points, and have -10 at the start of the game.)

* Skills: Mace & Flail will be are melee weapon skill of choice, mainly because of The Mauler and Diamond Eyes. Before those weapons are available, you can use maces you find early, then add the Hammer in the off-hand after class change. Wizardry and Divinity have most of the important non-combat spells, which is what we're looking for. You want 50 Wizardry because of the way the SP calculation works; game takes your highest spellbook skill, half the second highest, a fourth of the third, and an eighth of the fourth, but is capped at 125. If you have 100 Divinity and 50 Wizardry, that's enough to max this out.

* Spells: We're doing this build so we can get long duration spells like Missile Shield early while still having a good fighter-type later on.

One other little trick: Don't create this character before starting. Instead, create a Priest with Mace & Flail higher than Staff & Wand for the starting equipment, check the starter chest if you think you might want to reload it, then replace the character with the Dwarf Bishop. No need to buy starting equipment; just take the equipment that the starting Priest had and give it to the Bishop. This, in particular, allows you to start with a mace rather than a staff.

Multiclassing and spell progression is weird, see: levels in the new class stack with the old for spell progression for old spell in such ways as highest green power level, at least when switching to a natural caster. Also, there is a caster level penalty of four for the six gishes, and one for the four non-casters, effective immediately. This applies to all schools! i.e. a level eleven bishop, level five priest has an effective caster level of sixteen, for, all, books. (Except for learning spells, of course.) Bishops are absurd. I hope I didn't butcher that.

Dual wielding is worse than most styles, until past the point the game normally ends for most classes in a party of six. One exception might be a ninja, actually, where mauler/nunchaka might overtake martial arts before the game ends, but then there's just sticking him with a dread spear... The problem is that the accuracy/attacks & swing penalty is a percentage of close combat/weapon skill(s).

Sure, maces are great for priests and bishops, just like giving an alchemist the guaranteed shillelah early is decent. But slings get nine percent k.o. and then nineteen when maces finally give more... but do less damage, even with the penalty to ranged damage bonuses. Shields are good for their a.c. and maybe stat bonus. The resistances and skill bonuses aren't all that relevant. Whips are kinda awful otherwise, since they have the same penalties as ranged attacks.

The problem is that, for most of the game, damage is arguably more important than status effects. Of course, weight, skill increases, attribute bonuses, to-hit, and initiative bonuses are also important. Once effects go over fifteen percent, then they start mattering a lot more. Also, stacking stat effects, like staff of doom, Zatoichi bo, or mindblast. But it's still more gravy than meat, if you will. That's why the omnigun is rather terrible: all statuses, no damage. Disruptor is similar, but at least it's early, crock early—Which, for me, is around level eleven.

P.S. why would you ever rely on items for long-terms buffs outside of challenges? Unless it's to grind music/engineering via quick save/load abuse. Which I guess is nice if you like backfires. Or artifacts, I guess, but then there are scrolls of identify item… (Well, detect secrets, true, true.)

Fighter, samurai, or ranger, in that order. But, usually, I just give my Mook rangers polearms, make my fighters dracon, and I'd probably prefer shields on my samurai. I'd only use a Mook lord or valkyrie in a four giants playthrough, for divinity.

Slings have the *major* disadvantage of needing ammunition, which severely limits how often you can use the better ammo types, and also means your party is more likely to be encumbered since you can't just leave the ammo at home.

Also, Dual Weapons works really well if you get the Dimaond Eyes, especially if you have The Mauler to pair it with.

Whips are good for more traditional Bishops, as it gives them a ranged attack, allowing them to stay in the back row, while still allowing to use a shield for the defensive and/or speed bonuses.

Are you sure? First time I've heard of this.

(Would that mean, for example, that for example, a level 8 Bishop/level10 lord would be able to reliably cast X-Ray and Haste at PL 7, assuming the character has the needed skills and spells?)

I don't count instruments and (most) gadgets the same as other items because you get unlimited uses. For long duration spells, at least the ones you can get on instruments/gadgets, there's the fact that you can stamina cast them ,means they're basically free outside of combat, so you can use them as much as you want. If it's possible to stamina cast the spell at PL7, you can just keep trying (Shift+U) until you get PL7, and it goes quick.

Scrolls of Identify Item are only PL4, which isn't enough for some items. Also, Artifacts is good for consumables, and there are a few consumables that are strong enough to justify some investment, notably the amulets of Healing and Life (especially Life, which hard requires 35 Artifacts; I like to put points into a Valkyrie's Artifacts early because of this).

During the hardest and most annoying part of the game, Arnika Road, status ailments are likely more important. In particular, in this segment, I've actually found the Blinding Flash spell to come in handy, as it means I don't have to fight as many strong melee attackers at once. Of course, I don't ever use that spell at any other point, but at that one specific part in the game, the spell is actually quite useful. You could say the same about Terror.

(Worth noting that, of course, it's also possible to just run toward the next area if you can blind/fear all the enemies.)

Forgot another point: The spells you'd stamina cast outside of battle, including Armor Plate and Missile Shield, do not ever backfire. As in, as far as I know, they can't, or if they can, a backfire doesn't do anything other than play the backfire sound and, in the case of instruments, the instrument's failure sound (which sounds like someone playing terribly).

It usually ends up being Ranger for me simply because I find that I often want to fit a Ranger in the party, but often favor melee over ranged combat.

(Though note that a Samurai can cover Enchanted Blade and Missile Shield, as well as X-Ray later on.)

No class changing! I'm going with pure builds here. A Bard and Gadgeteer can be absolutely badass with a Light Sword and Light Shield (mediocre without). I'm OG (original guys, and gals).