If it's a case of "You get 1 power" and we can choose then yeah, that'd be awesome - normally warlocks suck balls, but this quest suits them perfectly.
The first level invocations all have a use, Summon Swarm is the allkiller, Dark Ones Luck, Miasmic Cloud and Entropic Ward are the defense and the others have varying usefulness - Beguiling Influence is a +6 to Diplo, Intimidate and Bluff.
Hmm, yeah - let's make finding Warlocks a priority. Wizards are a good place to start - the right magic can find them and Adventurer taverns will have them (there's not much else for them to do, other than rock out as diplomats)
They also have DR.
Other good things, with useful low level bonuses :
Dread Necromancer (DR 2/magical blunt) and awesome Familiar (Ghostly Visage)
Duskblade: Once we have some spells for it.
Barbarians - move speed boost.
Rogue - Evasion, SA, UMD.
Hexblade - Dark Familiar, Arcane Resistance, Mettle.
Ninja: Ki powers.
Psions etc: Powers that are convenient, flexible and somewhat subtle.
Troll - Regeneration - too tough for us, unless lucky + choker'd up.
Choker - extra move action, chokers are pretty tough one-on-one but is SUPAR IMPORTANT when when can take it, they're only CR 2 - which means that we should wait for a little while. They hang underground as well - if we can tak alligators, then we can take a choker.