My brother and I shared an account. He went unsuprisingly for a human Paladin.
I looked at the Alliance and found it boring to tears. I called it "variation on the theme of humans"- since basically you had the choice between: humans, small bearded humans, even smaller funky-colored bearded humans, and tall, funky-colored pointy-eared humans.
(there was no BE or Dranei at the time)
*yawwnn*
But the Horde! Past the underdog and cool backstory everyone already spoke about... What interesting character concepts! And the Tauren, Trolls and Forsaken- and even Orcs- are not found in your average fantasy MMO with their usual humans and elves and dwarves...
And, the Tauren.
Holy mother of jesus on rocket-propelled rollerskates, guys!
You can play an 8 feet tall armored battle cow! That eats meat! And that manages to look all soft and cuddly and deadly at the same time?
How is that NOT awesome?!?!?
And actually, I found the Horde races to also have an interesting characterization of the female gender toons.
Screw those stupid night elves in undies that will "dance 4 gold": what best for a player like me that happens to be of the female sex and likes the depiction of the latter in videogames to be as badass as the males and not overly sexualized?
F-ing Tauren that is.
I'm actually taller than any of the guy sprites 'cept male Taurens (and the occasional Troll doing their idle animation and strech to his full height), I look like a big, tall, horned ball of armor doom and my shield is so big an entire family of gnomes could use it as a raft.
Female Orcs are also very neat, badass, and they do look like actual orcs. I'm less keen on the she-Trolls that look a bit too much like a recolor of an human supermodel body shape with funky hair and feet, but at least they change from humans and elves chicks.
Now there are the BE, but at least the BE males are also very... so it's like a fanservicey race in all.
Draenei are finally really cool addition to the boring Alliance but the sexual dismorphism between the males and females keeps frightening me...
(how. can. they. mate. without. snapping the girl. in two? *shudders*)
On the alliance side, I did roll a she-dwarf and a she-gnome (A pink-haired ponytailed lil' thing I named Bubblegummie (Destroyer of Worlds). Cue in two swords three times her height

Liked her a lot, actually.)
But despite having all the good scenery (since Horde lands now are "Variation on the theme of "wasteland"), I found it a bit more boring, and maybe I just had some bad luck but people on the alliance side were less friendly and they didn't do battlegrounds at all (and that's what I like the more!)
So... for the Horde! And /moo !