From my experience, Salvador is probably the best all-round, while Krieg works better in some situations and worse in others.
Gaige has some fantastic abilities that exploit some of the best equipment, but her action skill doesn't work on some bosses I've noticed, and she doesn't have the survivability of the previous two as far as I'm aware.
Maya isn't fantastic, but she is very helpful regardless mostly because of Res, and personally the amount of Team Regen she can dish out is helpful too.
Zero is awful, and only gets worse with every level cap increase. I struggled to pick abilities by the time I was at level 35 or so, while the other characters all have abilities you wished you could get but couldn't reach at level 50. His action skill is almost worthless in multiplayer, serving only to help revive people really, and Res is better. IIRC, he does have an ability that works well with the infinity pistol, but it's nowhere near enough to stand up to the others. His melee tree is next to unusable even by the end of the first playthrough, even using Law & Order or any of the other good melee combos.
I have never used Axton, but I would put him below Maya myself, because although he's probably a little bit better, Res is far more useful.
But yeah. Krieg is just immortal most of the time, bypasses some enemy's damage resistances, but stuck to melee or very slow ranged attacks and at least back when I played it, he was prone to glitches with his skill... and Salvador is just broken... Stupid damage, stupid health regen, magazine regen, stupid fire rate and two guns to boot... but he can die, and sometimes he has to wait for his action skill a little.
Those are my impressions at least.
PainInTheAssInternet said:
I haven't played B2, though my roommates own it.
I can say that I found rocket launchers practically useless in B1. I was always puzzled. For context, I had corrosive, explosive and incendiary rockets using the soldier class and they all seemed to do minimal damage compared to my pistols. To the best of my recollection, the stats boasted 400 damage for one of them.
I think balance will always be an issue in games where there are so many options. I think that's why COD has such an issue with it; there are simply too many options to account for.
IIRC, you were only really supposed to use rockets on the Berserker because the ammo regenerated every time you killed something. They were good for AoE damage and somewhat for accuracy at a distance if you were focusing on shotguns, but without regenerating the ammo they were never that useful.