Our warlock pulls a minimum of 6k DPS on patch every week, so from what I see I say lock. But if you want to PvP too, I would suggest going with Rogue, Ret Paladin, or DK as they are very strong in PvE and PvP at the moment. It's all personal taste anyway, and whatever is the most fun to you I would go with. If you play it well your DPS will be just fine.