i started alliance, tried hord after reaching level cap. After trying Horde I never looked back. Besides how else can you kill Gnomes? Overall it felt as if horde worked better as a team and contained more mature players. Being over two years since I've touched the alliance side, i'm sure it's pretty much the same now thanks to Blood Elfs.

To me the horde quest story lines have always had better stories imo.

When it comes down to it the choice is easy however.
Alliance = lets frolic in glee with our cute characters that look pretty
Horde = Think I look ugly? wait until i'm finished smashing your face. It’s all about who’s large and in charge!
Lol before the flames start, please realize I’m joking. Or am I?