Faction Superiority

I've been leveling horde and alliance toons on icecrown for awhile, and I've been wondering.

Which faction is better? Which tends to be more successful for pvp and pve? Are they about equal? Does it matter? Let me know what you guys think. I've been wanting to get some characters up for city raids and probably some actual raids but I'm not sure which faction I should focus on.

I always have been play as alliance, and they always owned horde, but now....It is nearly impossible win bgs..