Horde, because my friends played it.
Alliance. Because let's face it, Jaina is a douche in MoP but less so than Garrosh.
FFXIV - Maduin (Dynamis DC)
In vanilla all the Horde races were ugly, so went Alliance.
Originally had both Alliance and Horde in Vanilla, but ended up going 99% Alliance because Horde players were obnoxiously aggressive and the Horde quests back then made the faction seem clue$&@/ed.
Help control the population. Have your blood elf spayed or neutered.
I like both factions, I play horde tho, because of a friend that made me play with him years ago when I started....
Choose horde on a dead realm, then my friend asked me to play with him on alliance side on another servers, he quits a month after that...
I started as orc but abandoned it at around lvl 20 and went worgen because my friend played alliance at the time.
Horde struck me as more interesting and nuanced. Humans were boring, Dwarves were okay, gnomes had potential but Blizz treats them like a joke, and the Night elves... well they were alright but then they got gimped by Blizz :P
Twas brillig
Alliance, I wanted an Elf. Horde had no playable ones at that time.
I also compared the landscapes, and found the alliance side ones visually more esthetic.
Today, years later, I play both sides rather equally. Yet the beauty judgment remains for me. Alliance architecture and appeal is more esthetic in overall.
Horde was ugly.
Horde looked evil.
I wanted NE and human and dwarves, LotR races that represent "good".
Horde, out of necesity, they had undead.
I thoroughly disagree with their philosophy otherwise.
Alliance, because they have dwarves, and don't have genocidal abominations in their ranks.
Horde, because of tauren. Rolled undead for my first char though, hehe.
My first was a troll hunter, and I chose it because my friend who got me into the game was horde (tauren). I eventually went alliance with another friend for PvP and now I really don't care about what faction I'm on. It's all the same; trade chat is still retarded no matter what side you're on.
I started out as horde mainly due to their diversity in character designs. Horde just had so much more variety than the alliance and still do. I didn't care about racial abilities because those only helped a little what I worried about was how the toon looks. I'm going to look at this character a lot so why not pick a faction with more variety?
Alliance had Night Elves so Alliance. If I were new to the game and starting now I'd probably be Blood Elf since Blizz has done a great job with their story while thoroughly ruining the Night Elves.
Horde, my friends who got me into WoW played horde, and since then it has just been "home"
Tried alliance a few times, I like their lore, but I'm too integrated into the horde to leave now :P
When I started I played a Human Paladin. I choosed Alliance because everyone I knew played it. Now I am horde though
Horde, specifically Forsaken because I always choose the most monstrous looking race I can. Undercity is dark and quite honestly my favorite city next to Stormwind or the Gilneas capital (name escapes my mind). The abominations, the music, Sylvanas, (at the time) the Dreadlord, the flying bats, and it had the coolest place for magic classes (specifically Warlocks) so I felt so happy there. Tirsifal Glades is also very nice looking to me.
I also played Undead in WC3 so they were a favorite from then. They can hold their breath underwater which is very cool (redundant for a warlock but still), they can eat people, and they just aesthetically look cool to me. Also their dance and laugh is amazing. If I ever wanted to look normal, I had the blood elf orb :3
Also because Forsaken are the superior race and they will blight nuke everyone, starting with the disgusting creatures known as Gnomes, followed by the delicious tasting Tauren steak beasts.