Ever since I first played through the game like 15 or so years ago, I mostly gravitate to the same party, being:

Me - fighter
Ulora/Phaedriel - archer (the only companion swap in the game I usually do, Phaedriel is just a better archer than Ulora when you meet her)
Gyorn - fighter
Naidi - archer
Gloern - fighter
Merik - Nature mage
2 mules (right away from Stonebridge).

3 fighters, 2 archers, 1 mage to heal/buff and add supplemental damage when able. 2 pack mules so I can pick up and sell absolutely everything I find with minimal backtracking, and also to keep the XP distribution of the party tighter. 5 or 6 fighting members seems to be optimal for somewhat keeping up with the gear and spell requirement curve in single player. Any more, and wearing top end gear would not be really feasible.

I find more mages extremely tedious to manage/use efficiently, on top of being pure glass that falls over instantly the moment an enemy looks in their direction. You also have to target farm XP with them or they fall extremely behind your fighters/archers, so having to do it with 2 mages would be very tedious. Gearing one mage is also much easier than two. I always think hard of swapping one mule for Sikra when I get to her, but at that point, I just don't bother and finish the game with the main party. Also, having the final party composition from the moment you meet Merik feels nice. Adding new party members so late in the game doesn't really feel good. The paid ones are very expensive late in the game and non-paid ones are kind of superfluous too.

Merik is probably the one character I'd never drop, as he feels pretty integral to the main plot.

So, anyone willing to share they group composition for the campaign?

I just entered the DS specific thread, because I started DS1 a few days earlier, and I wanted to see what's in this thread. I will play all DS games back to back. It will be my second time playing the series, after 3 years I think. I will post their plots too, if I manage to write them in a right manner!
To answer your thread's question, I soloed DS1 and DS2 at the first time and I'll do the same now (normal difficulty, archer). I accepted story-wise companions (e.g. Ulora, Gyorn, Gloern), only to release them at the next establishment, and I had only packmules following me. Currently, I'm 13 h in DS1 and I just got in Glacern.

Huh. Have to wonder why anyone'd want to do that to be honest. The party aspect is basically the point of the games.

But to each their own I guess.

I realized that I didn't remember that correctly from my first playthrough. I did soloed DS1, but in DS2 (while I was the only human in the group) the pack-mules do fight! And do very serious damage, if fully matured. So, basically, I wasn't fighting alone in DS2. In DS1 I was fighting alone. I'm currently in DS3.

Edit: In DS2 I was leaving the 3rd animal in the inn, and I was taking occasional companions, only when it was time for their personal quests, e.g. Amren, for the mushroom circles.

It's a decent enough game. If you completely forget what Dungeon Siege is :D

Gameplay-wise, yes. But the interesting lore is still there. I'm currently 8 h in. At the Heroes' Crypt, where the dead Heroes (including Lady Montbarron) from DS1 were interred.

Well, all the games are quite enough apart so they could choose where to loosely connect them.
DS 3 happens 50 years after DS 2 and 150 years after DS 1. The crypt was a nice callback to DS 1 I guess, although I don't really remember any references at all to DS 2. Happening only 50 years before DS 3, I would have expected to actually hear more about that in the game, rather than the distant history of the Seck threat. Although it's true DS 2 took place quite a distance away geographically from Ehb and not really sure whether Ehb felt the 2nd Cataclysm at all.

Wow, so happy to find someone who still plays this game in 2024.

You are absolutely right that mages in DS1 are terrible glass cannons.
Nonetheless, I like to have 2 nature mages. That way, I can have one of them cast a damage spell to gain xp, while the other is on healing duty. And switch them around. In an emergency they can both heal.

Even so, they're a nightmare to level up for sure, as you're stuck with Flash for such a long time. Great damage spell but the short range makes it really dangerous. So what I tend to do is get Zed early, add Merik and then replace Zed with Andiemus later. Once you can cast Multispark, levelling is not as bad anymore. In between, Ice Blast (casts 5 ice shards) is a reasonable alternative for flash for levels 24-29.

Anyway, I agree that a party with melee/archers and a nature mage or two is probably the strongest. Compared to your party, I like to have 1 or 2 fighters and fill the rest with archers, because 3 fighters tend to get into each others way. Having 2 fighters works well with the box formation, where they can form a neat frontline - until swamp witches cause utter chaos, at least.

That being said, I am always tempted to go heavy into combat magic in my party because fireballs are cool. And the summons are nice as well (especially the darkling - good ranged damage, good health). In the endgame you may just be able to cast Bomb. That's an amazing spell, I think it's the highest damage you can get in the single player game. It is better than it looks on paper. It seems the particle damage pierces armor. (I love the goblin grenade launcher as a backup weapon for the same reason -- during tests I found it actually deals more damage than a goblin flamethrower.)
With combat magic, you have the option to have a character start as a melee fighter and then switch to become a mage, so you can wear better armor and get more health, at the cost of mana. Like Boryev did. The combat magic spells are less mana hungry than nature and you also get Mana Chant.

Getting into specific characters, I often turn Gyorn into whatever I need to round out the party. He's such a low level that you don't lose much stat-wise, and pretty much every character benefits from strength anyway.
If I need a pure fighter, I prefer Rusk over Gyorn. He starts out with just a little higher strength, making it much less of a pain to level him up in close combat in Wesrin Cross.

By the way, do you impose challenges on yourself? One handicap rule I enjoyed is to forbid myself to use health potions or to reload. That makes Normal difficulty a lot more exciting. Monsters can't use health potions either, so it makes things a bit more fair, although it's a little tedious to heal up at the start.

I have zero issues with 3 to be honest. Some redundancy is also good in case somebody goes down, so you still have a frontline when that happens. Also of note, all my campaign fighters are usually 1 handed + shield. The damage of 2 handed weapons is just not higher enough to justify them. They eventually do outscale 1 handed weapons enough to be worth it, but I only found that to be the case on the last difficulty in the multiplayer world. That's because those (Grenade Launcher, Flash, Explosive Powder, Bomb) do damage in a massive number of very small instances. And armor is much less effective against those. Damage cannot be reduced below 1, so even if the enemy has a ton of armor, it still deals good damage. And they shred low armor targets, which is why they are so good for levelling. The way they deal damage also tricks the XP awarding algorithm to give more XP than usual for damage sources that work like this. I multiclassed a bit in the multiplayer world, when I was playing through it. Played through it single player, started as a fighter, and later levelled up CM and NM some. Specifically for Triple Strike in CM and Regeneration in NM. With a single character, you need all the buffs you can get access to. The INT was also good to be able to use Spell Books with bonuses. Played through the multiplayer world on normal, because hard would be an extremely tedious chore with just one character.

But I find there is not really enough space to multiclass in the single player campaign. Rusk has that 1100 hiring fee, which always made it really unappealing for me to get him. At that point in the game, I usually want 2 mules and some gear from merchants for me, Ulora and Gyorn. Not really. Though I always play on Hard. Enemies hurt a lot more on that difficulty and also can take notably more punishment. It applies a 0.85 multiplier on damage your characters deal and a 1.45 multiplier on damage enemies deal. The lowered damage output of your party makes enemy armor more effective and enemies can punch through yours much more effectively. Even in the late game, the Seck for example chunk your frontline fighters VERY hard even in top gear. Hard is great for making the game feel like it always properly scales the challenge as you progress. Normal, I find, fails to keep up and the game becomes too easy eventually.

I do use potions, but no, I do not reload, unless I actually fully wipe. There are Resurrection scrolls and spells for a reason.

One notable thing about difficulty is that if you play on anything below Hard, weapons receive a significant markdown in their sale price. On Hard, they provide some serious cash when selling them.

Right, I can see the value in having a more resilient frontline. Maybe I will try your setup in my next playthrough. Since you go with just a single nature mage, I am a bit surprised your Merik can level up fast enough that you don't want to replace him with Andiemus. I had a number of runs with 1 nature mage and ended up replacing him every time I did that.

Yeah, 1 handed + shield is the way to go. I didn't play much multiplayer, good to know that 2 handers are at least worth it at some point. One small exception is the rake just past the bear cave, that's the one 2-hander I usually use for a short while. :) That explains it, I rarely buy any mules and just leave the cheaper stuff on the ground. Yeah, the point of no reload is that a wipe ends the game.

Oh by the way, have you ever tried the Lands of Hyperborea mod? It is basically a completely new game, using the DS1 engine. Really excellent, I can recommend it.

Me neither. I just played through the multiplayer world in single player :)

I usually keep Merik for sentimental reasons. He is probably the most story relevant companion in the game and leaving him there right after freeing him just feels weird :P

And with Flash, he can keep up pretty well. I manually swap between offense/healing. In tough fights, he's full heal spam, but when just cruising around and killing small groups of regular enemies, he can just keep spamming Flash. Benefits of a 3 man frontline that can share punishment and thus doesn't need full support non-stop. Because yeah, 1 Nature Mage on heal duty only would fall quite behind. If all else fails and he still does fall behind, you can just solo kill enemies with him for a while to catch him up. Just find some ranged enemies, have melee draw aggro, post Merik behind melee so the shots get intercepted even if the enemy retargets on Merik and grind XP.
Oh, in that case, I'm not actually sure to be honest. Don't think I've had a full party wipe happen. It is quite difficult to get all your characters killed. Only really possible if you get AoE'd really hard. If my frontline starts crumbling, I usually full retreat. You can then micromanage your ranged characters to clear basically whatever with hit&run tactics. And as long as at least one character survives, you can recover.

The most problematic spots are Bandits (who hit like a truck), the goblin boss (one misstep=death) and the Seck.

I did not. Might look into it. Think I heard about it in the past, but never played it.

Yep. And came to exactly the same conclusions. First played through the vanilla game, including Yesterhaven and the multiplayer map and only then installed LoA to play through the expansion (and Return to Arhok). I talked a bit about it here:
https://www.gog.com/forum/dungeon_siege_series/enabling_ds_1_2s_expansions_on_gogs_version/post62

All the expansion stuff being added to the original campaign really skews the overall balance. They also changed the formula for armor vs damage or that skill levels for melee/ranged now affect the damage you deal, making the game noticeably easier overall. Even though they tweaked some of the formulas, they did absolutely nothing to adjust the non-expansion campaign content and it shows. I included some finer details in the linked post.

Late response, but I would go a step further and say that LoA is badly balanced even for the LoA map itself. If you give the giant (Naj?) a staff, he deals absurd melee damage and if you have him in the party plus a nature mage for healing and a combat mage for haste + triple strike, you tear through the game like a knife through butter. There is a guaranteed staff in the game with high melee damage (dropped by that encounter with witches and lightning).

So, I replayed the original game on hard, with the extra restriction of never drinking a health potion. For the sake of variety I played the single player mod for the Utraean Peninsula, a nice recent fan-made addition.
Didn't finish yet, but my party is now
1 melee (farmgirl)
1 ranged (Ulora)
1 high strength nature mage (Byorn)
1 high strength combat mage (Gloern)
1 low strength nature mage (Andiemus)
With high strength I mean strength 24+, which you reach late game if you switch from melee to magic at level 18. I really think this is the sweet spot and highly effective in single player. You get a mage that isn't nearly as squishy, with more HP and able to wear any plates that an archer can normally use, up to quarterplate. It also gives you access to more/better bonuses to magic on your items. My high strength mages could easily shop / find items with +2 magic on their boots, gloves and shield and Gloern has +3 combat magic on his armor, too.

The only problem is that Gloern is now in that awkward spot where fireball has stopped improving and no other combat magic spell can match it. Flame blades is a pretty crappy spell.. but he will be able to cast Bomb before the game is over.

After this run I'm itching to replay Lands of Hyperborea. You will love it. It's harder than the original game: "easy" mode on LoH is about the same as Normal mode in Kingdom of Ehb. The story is awesome. The spell system has been revamped, spells are harder to find but more of them are worth using. You can craft items and steal from chests by unlocking them. And you can even rotate the view to look straight ahead.