Alright, well I started playing a few months ago because my buddy made a very convincing case... Anyways, I now have a Lvl 70 Draenei Mage on Bonechewer (name: Icipher). So i have seen the world under the Alliance, on a pvp server... Very very difficult to try and level, STV is definitely off-limits, but anyways, back to my point.
The Horde have a much easier time surviving in the world (forget BGs for now) because they are usually "older" players who have had much more experience in the gaming world. Most allies that I have met on my server are under 25, therefore proving my point a little more.
To whoever said "if you want pvp gear, roll horde," you are almost correct. If you want marks from AB, WSG, and EotS, roll horde. If you want honor, roll alliance. Something about allies that gets me, is that we always win AV. It just doesn't make sense to me.
The one thing that I did notice from playing on a bunch of different servers with different irl friends, and also from the site wowjutsu.com/ Alliance guilds are way better at the PvE aspects of the game. Way better. I'm not saying I'm the best player in the best guild, but my guild is 26th on our server, and 337th in the US. That's pretty damn good.
So imo, if you wanna raid, roll Allies, if you wanna PvP, roll horde