For questing I've found Affliction warlocks to shine here. Basically Dot and go. While mages in close range instant done everything in a couple of clicks, wont be long before you need to drink. Lock dots however are cheap. Plus life tap. So a kill quest you can just hit auto run and hit tab and use a cast sequence macro to have the all three instant cast dots on it and your good to go! Very mobile, always moving team. That's what I liked about it. Unless your in an instance you never drink with life tap and heals.

In PVP you see someone, hit your cast sequence like any other mob, three times and your done. They can do whatever they want but those 12 dots will kill them in a few ticks. It's also a bit more joyful to watch as you get to see panic set in and then finally acceptance as they just stop running and stand there to prepare for the corpse run.

If enough people fight you and you die, you get to soul stone back up and dot the survivors.

Post BC wouldn't recommend. But that's another conversation for another day.