this is a hard thing to decide, but I'd say my list goes a little like this (mostly based on BG / IWD series and 2nd edition):
1. Halfling - thief (subclass doesn't matter, they're all nice to be, just love it to be sneaky ninja-lika and to find/disarm/put traps, open locks/doors, etc... the lore bonus is also nice)
2. human / elf - Mage / Sorc (I used to be more of a fighter person before, but I learned to love the classes based on spellcasting/other ranged attacks / sneaking )
3.Human/elf / half-elf - Cleric (sure, not as versatile as the druid, and with less offensive spells, but better defensive party players, still have some good offensive stuff, neat-o VS undead, I really find Turn Undead to be good)
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Human - Paladin (either Inquisitor or Cavalier)
A Cavalier gets are quite nice in the aspect that they get such things as immunity to fear, poison and charm effects, + fire / acid resistance set to 20%, not to mention their hit + attack bonuses vs demonic and draconic creatures, I found that great
An Inquisitor is as we all know, a very strong paladin, and I'd say the lack of casting priest spells is countered by their instant cast spells, among them dispel magic, which is quite nifty with no casting time on, more than usual that is.
4. Human - Monk
who can't love that class? bonuses and feats like no other class
5. half-orc - Barbarian
prefer this class before the fighter classes, with the exception of:
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Human/elf - Kensai
Kai, Kai, Kai, Kai, Kai
that's top 5. for me (though it's 8 classes, +/- subclasses ^^ )
they're all pretty close to eachother to me though, I'd gladly pick up any of these classes anyday
never learned to like the bard though, maybe I should try it out sometime
BORK!