I can’t compare all the races now it just matters which racial passive works with your chosen class that you have. For example, as rogues on the alliance, I think that night elves and humans do better than the rest, just the way I think that undead works better for priests and warlocks at the horde.
So when you’re choosing either to play alliance or horde just focus on things like looks but also racial passives and you can take into consideration even the battlegroup for the PvP and PvE.
You can find a link here for the battlegroups to find which realms work together for dungeon finder or raid finder or random battlegrounds.
And it’s simply your choice to decide either on which realm you wanna play horde or alliance it does not matter. I found out that the horde can be better in PvP than alliance in some battlegroups so if you know one faction is better than the other chose the best.
The thing is that I’m asking, what do you want to be, a filthy monster who plays some slacking horde archeotypes or just a friendly neighbour who is all sweet and kind but most vicious of them all, Just think about it for a second.