My wizards and rangers are generally elves unless I want to play a specialist, and my fighters and clerics are usually dwarves unless I want to dual-class. That's solely for the dex bonus and saving throw bonus, respectively. One of the biggest bonuses for humans in AD&D, which is that they don't have any level restrictions, isn't implemented in any of the IE games, so they just have to stick with dual-classing and playing paladins. I play elves and dwarves fairly often. Elves also get a small amount of race-specific dialog here and there, which is more than most other races get.

I've never actually played a gnome, but I have played several halflings, all of which were thieves of some variety. I personally like half-orcs a lot, but their multi-class options are very limited and they can't romance anyone, so they generally only get to be fighters or barbarians. Unfortunately a lot of the special racial abilities aren't implemented in the games, which makes races like gnomes and dwarves less exciting because their bonuses don't really fit into a cRPG very well.

Elves get the constitution penalty, halflings get a penalty to strength.

I use gnomes as pure illusionists actually. I know, I know, I miss out on a few really powerful necromancy spells by doing so, and once you get into the level 20's power wise you lose out on being a pure (non multi-class) mage, but to be honest I really like playing more of a manipulative, de-buff mage than a directly damaging mage. I may have a small problem with taking pleasure in turning dragons into squirrels....

As for halflings and dwarves, I've never really got into either. I'm not really a warrior type, although to be honest the first time I beat TOB was with an undead hunter (who was obviously human). I tried playing a halfling bounty hunter once, and I tried playing a dwarf barbarian, but I could never get into either. That said I guess it all depends on what you like from the game.

I usually play either a Human character or a Dwarf. I love Dwarves, but the 3e rules spoiled me, since you can play as any class with any race. I use Dwarves far more often in games that use that rule set. But I still like them in the AD&D games too.

I play non-humans almost exclusively. My favorite is a gnome fighter/illusionist. They get to specialize as a multi-class and get the intelligence bonus. Plus there is some kind of size bonus too. My favorite thing is that the spell sunfire, stone skin, and mirror image take on a whole new meaning. Tensers transformation and the fire shields are good too.

Other than that I like the half-elves and elves for roleplaying reasons. Same with a dwarf fighter/cleric.

My most played race is half-elven, because of it's class options: a ranger-cleric can only be half-elven, bard's don't benefit from dual-class anyway and get a charm/sleep resistance bonus (with BG2 fixpack, it was missing in the vanilla game). Same reasoning goes for any single-class character you don't intend to dual-class.

Elves are my most liked race, but they don't have all class options, so I often end up making half-elves of characters I'd rather play as elven. Nice class for an elf is fighter/mage, not as powerful as the gnome fighter/illusionist, but the longsword/bow to hit bonus is nice, especially in the beginning of the game (BG1) and is nice from a role-playing perspective: my ultimate fantasy hero (and earliest AD&D character back in my Pen and Paper days) is a spellcasting, sword- and arrowslinging elf (remember basic D&D, the Elf class was practically an elven fighter-mage.

Humans are third, if I want to play someone feeling very close to myself, I play human, though I don't often dual-class: for the most favourable dual-class options you often end up playing most of the first game as a single-class character (especially for fighter>something else dualed at level 7 or 9, you end up playing most of the game as a plain fighter, which I find boring).

Gnomes are my fourth favourite, either as fighter>illusionist or single class illusionist.

Finally I played a half-orc barbarian female once. She was a mighty slasher.