Go Demonology. With my 5 locks, it's like a blender and you only have to put one DOT on just about anything (including other players) and the pets will do the rest. With the new addition of Fel Synergy, very rarely are any of the pets under full health. I can't wait for WOTLK and the ability to add the Siphon Life DOT to the arsenal. Should be a strong PVP spec for arena as well.