Least liked (becuase they're useless) would have to be Jahiera, Faldorn, Quayle, Yeslick, Alora, and Tiax... with the exception of Montaron and Coran for their superb stats suitable for both, all of the multi-class NPCs are crap, not to mention annoying and ugly
The NPCs I can tolerate, and can be quite useful are Garrick, Shar Teel, Kagain, Branwen, Montaron/Xzar, and Ajantis... none of these characters really stan out but fun to take along once in a while.
The NPC all stars have to be...
Fighters:
Kivan - well balanced in both ranged and melee.
Minsc - Always good for a laugh, and is in fact the strongest NPC I believe + berserk.
Coran - Bracers of archery and longbow of marksmenship for this guy, steady flow of damage to aid your tanks in bringing down the big boys, excellent in melee as well.
Clerics:
Viconia - unless you are a cleric, she has to be the best (perfect for wearing the ankheg plate).
Thieves:
Safana - strong and agile, and with her in your party, it's a good idea to dual-class Imoen without worrying about losing the best theif.
Imoen - without saying.
Skie - late game substitute for Imoen.
Eldoth - need him if you want Skie, and why waste skill points for pickpocket with the others. (and I know he's a bard, the more magic missiles the better.)
Mages:
Xan - better for support spells than the cleric NPCs, moon blade.
Edwin - Cleary top-notch, 12 magic missiles as mentioned earlier with RoWI.
Dynahier - Just as good as Edwin, even better actualy if you want to have a Reputation of 20.