My first group was 4 warlocks. I've since moved on to other stuff, but I always log into my locks when the Horde on my server are attacking of of our capital cities. I've stood in Stormwind/Ironforge right outside the Deeprun Tram portal and wiped full city raids with Meta+Immolation Aura and SoC spamming.

I'm a big fan of DKs right now... but for pure PvP AoE damage I don't think anything beats warlocks. SoC is just ridiculous.