Nord. Almost always Nord, but I have my reasons:
1) Argonians & Khajits are just too hard to RP for me. They aren't allowed in cities (okay, well Argo's are allowed in Riften without an issue), plus the tails annoy me (especially since they keep moving after your dead), although I love them as NPCs.
2) Imperials - just can't get in to them, although they have the most extensive cannon to call upon. If I wanted "handsome" women, I'd make a man.
3) Bretons - short and dumpy, can't stand 'em.
4) Mer's - people in Skyrim don't like elves. Again, RP issues. Plus never, ever, ever Dunmer - those red eyes just FREEK ME OUT!
5) Orcs (okay, so they should go under Mers). Love their combat abilties, but can't get over the pig face. I like attractive, not frightening!
6) Redguards - I like Redguards but have always had an issue with them being the only ones that start out as dirty (they default to being covered in filth). Plus the entire attitude is that their not as good as other folks.
I guess I play Nords 'cause I like pretty people that look like me.
It's shallow, I know, but they gotta be great looking and wear the right stuff for me to want to play them.
Y'all are right though that, in the long run, unless you're a beast or mer, it really doesn't make a difference what human you play, it all equals out in the end.
I play human because they're the only ones that are accepted in Skyrim. It's just much easier to play the other races in Oblivion.