I am thinking of maybe giving Ultima 3 another quick playthrough, and I will need to choose a party to use.

I do, however, have some constraints:
* Will (I think) be playing the DOS version with the upgrade patch. Autosave wiil be left enabled (so I can use an exploit that requires it), and the gameplay fixes will *not* be used *(I want to keep the gameplay as similar to vanila as possible here). (Note that the version does make a difference here; in particular, the Amiga version has better rangers and the NES/MSX version has worse druids.)
* Will be using a balanced party, 2 fighter-types and 2 caster-types, with no duplicate classes.
* Fighter-types need to be Barbarian, Paladin, Lark, Thief, or Ranger. If there's a Thief, there will not be a Barbarian. (Barbarians are not as good thieves as Thieves, and they don't have any other advantage over Paladin, so a Barbarian/Thief combo is rather pointless, since you need only one character to act as a thief.
* Caster-types can be Cleric, Wizard, or Druid.
* I do like having a Ranger and a Druid in my party, for whatever reason.
* In the long run, I prioritize Dexterity over Strength, so Elf and Fuzzy are the preferred races; everyone who isn't a Cleric will be one of those two races. (I think I'll try Strength in the short term and see how that goes, but that doesn't affect the race choice.)

So, any suggestions what classes to use?

(Note that this is not my first playthrough; I have played this game many times, so I already know where things are, and I'm not even looking at anything unusual party wise.)

It's difficult to remember as I haven't played the game in several decades and complted it without the manual but does the party make-up really affect the gameplay that much?

(This post did come rather late; I already played through most of the game and have moved on to other games.)

Party composition does affect the gameplay significantly. For example:
* Cleric spells are very important early on, as it allows you to safely open treasure chests, as well as providing healing without having to go into a dungeon and find a fountain. (With that said, at higher levels using the fountain is really the best way to heal.) Druids, with their fast MP regen, are great for being able to use lower levels spells like these more frequently.
* In some versions (the IBM PC version being one), having a thief-type to open treasure chests is a lot faster than casting spells, once their DEX is high enough; this is, of course, assuming you have enough HP to eat the traps. (This doesn't work so well in the Amiga version, unless you take advantage of that version's streaky RNG.)
* Having someone capable of casting the ladder up/down spell is very important, as those spells make it so that you don't have to worry about navigating the dungeons. (Some players might find it fun to work their way through the dungeon without these spells, however.) Only Clerics and Wizards start with this spell, but others can learn it later.
* Clerics and Wizards, after increasing their casting stat, gain the ability to cast spells of mass destruction, which can make battles much faster (but it takes a while to get your MP back).
* Only some classes can use ranged weapons (other than daggers, which get used up), and ranged combat really dominates in this game (except in the final area, where no ranged weapons will ever hit).

My go-to party is Ranger, Paladin, Cleric, Wizard. I usually make the cleric a Human, beyond that, I never care much. If I'm willing to go with duplicates, I will replace the Wizard with a Cleric - the extra healing and utility is amazing, and the Cleric's mass destruction spell is OK. Situations where I really miss a Wizard are quite rare.

I can't stand Druids. I hate the very concept of a dedicated caster who cannot use the top end spells. Especially given the significant overlap in spells Druids can use, and the fact that the best Wizard spell they get is literally pointless for a class that can already cast Cleric spells.

Because I made a typo. I meant Human for the Ranger.

The thing is, Druids are better at using the low level spells because of how quickly they regenerate MP. This means that:
* They can heal every 5 overworld steps (instead of every 10), or every 20 town/dungeon steps (instead of every 40).
* At max stats, a Fuzzy Druid who has just run out of MP will be able to cast a long lasting light spell (because the short one is almost useless with its short duration) after only 88 moves, as opposed to the 160 it takse for a Wizard (and 180 for a Cleric); this is significant because the light lasts 255 moves (IIRC), allowing the Druid to spend their MP on other spells as well, like the ladder up/down spells. (For a Bobit Druid, it takse only 84 moves, but I prefer Fuzzy for the 99 AGI and the increased Mentar damage.)

With the faster MP regen, having a Druid in the party feels like having two spellcasters in the party at once, with the only downsides being the lack of ranged weapons and the lack of high level spells.

With this said, this only applies to versions that are similar enough to the DOS version; certain other versions have differences that makes Druids not worthwhile in them:
* In the Amiga and Atari ST versions, Rangers get the same fast MP regen as Druids (except for the fact that INT and WIS are checked in the other order), making Druids obsolete in that version.
* In the NES and cartridge MSX versions, Druids do not get the fast MP regen, making them rather pointless (except for the fact that the 0 MP spells are really good in these versions, and Druids get both of them).

While true, my party has 4 casters, three of whom can cast Cleric spells in some form. That's enough MP regeneration. Especially considering that torches are dirt cheap, so the light spells are redundant. A Druid can heal twice as often as a Cleric, and can cast ZXKUQYB 100% less often. I'll take ZXKUQYB, thank you.

Druids have real advantages, I just don't think they compensate for having no access to a general purpose mass killing spell. Also, both rez spells, the big heal (not worth the mana usually, but still situationally nice) and the mapping spell.

In the early game, before you've managed to boost your stats, a Druid can still heal twice as often as a Cleric, and both can cast the unpronounceable spell the same number of times (that is, 0); hence, that comparison doesn't actually matter until you've had a chance to get over 5,000 gold (don't forget the cost of keys!) and get into ambrosia (which requires a ship).

It is rare that I have a use for one of the resurrection spells; the game gives you so many hit points, relative to both damage and healing amounts, that you aren't going to have characters unexpectedly die (and you don't get crisis situations that often either, making the big heal not so important), and can therefore just reset the game if anyone comes close to dying before the game autosaves on you. In my most recent partial playthrough (I didn't do the final area), I believe I had only one death, and that was of a throwaway character in order to glitch myself a ship. Thing is, you should always have enough time to heal a character before they die, and again, the druid can use healing magic more consistently.

Also, the mapping spell can be replaced with gems once you reach the point where getting money is really easy.

One other disadvantage of a Cleric: The Cleric has no reasonable general purpose attack until you get to Ambrosia to raise their stats. Both Wizards and Druids have attack spells that can be used to get a little experience from enemies early in the game; Clerics lack that. In my experience, Clerics are lacking in XP until you get the big spells, while Druids get more XP early on (but fall behind later).

Interestingly enough, there is one thing to note about the big heal spell; for a Fuzzy Wizard (the only non-Clerics that can cast the spell), the spell is more efficient than the weaker one; unfortunately, that will leave the Wizard unable to cast significant spells for a while (having to spend 95 MP on one heal will do that).

By the way, Wizards have one nice advantage over Clerics, the Necorp spell (70 MP) will reduce all enemies to 1 HP. This means that you can cast this spell, and then have other characters who need more XP pick off the enemies one at a time.

I intentionally did not get the Mark of Kings in my partial playthrough; I am wondering how the final dungeon will work with only 550 HP (or 500 HP if playing the Apple 2 version) per character.

In the Cleric vs. Druid debate, I go with the late game power of the Cleric over the early game easy sailing of the Druid. It is 100% true that a Druid is almost arbitrarily superior to a Cleric in the early game. However, raiding the Snake dungeon gives a shocking amount of gold quite easily, even very early on - and once you have a lot of gold, getting your Cleric a good mana supply isn't hard.

Druids aren't a bad choice, they just aren't *MY* choice. I choose what I enjoy, which is the crushing power of high level mass destruction spells. I willingly accept that my Cleric won't be particularly effective until I can go to Ambrosia, and will probably be an active liability until I can get some Exotics. Once I have Exotics, no reason not to put the Cleric on the front line to get some experience in melee. All non-Wisdom stats go to Dex, of course, so I can actually hit things.

It's worth noting that you don't have to use the same party for the entire game. You could, therefore, use the following strategy:
* Start the game with a Druid (18 INT and 22 WIS), who wil be very useful early on.
* With the druid in the party, keep going until you have at least 4500 gold and 2 keys, along with a ship.
* Remove the Druid and add a Cleric (25 WIS, must not be an Elf) to your party.
* Go to Ambrosia, and raise the Cleric's WIS up to at least 70.

Incidentally, my dungeon of choice to loot is Perenian. My strategy does need at least one character with 20 MP, so a Cleric or Wizard is actually needed in the starting party. Perenian is nice and close to the start, doesn't require any moongates or ships to reach (or the 30 MP Wizard spell, for that matter), and I don't have to go below B4F to get the chests I need.

By the way, have you ever tried using a thief? I find that a 99 DEX thief is very good for opening treasure chests without triggering too many of the traps, and opening chests with the "G)et Chest" command is faster than using spells to open each one. (In some versions, like the Amiga version, be aware that poison is slow, and traps can be slow in some version. Also, in many versions Bomb traps deny you the contents of the chest, but the DOS version doesn't seem to be one of them.)