Affliction (naturally), and just a couple of observations I've made:
-keybind soul burn to teleport and healthstone. Both are incredibly useful.
-glyph of shadowflame. That plus sb/tele is an amazing gap opener.
-gear. It seems that locks are more dependent than most other classes on gear.
-silence DKs.
-soul swap, early and often
-you can teleport without LoS restrictions THROUGH bridge in blade's edge arena (me and my arena partner started laughing our asses off)
-curse of tongues on casters
-shadow ward works against DKs and hunters
I'm sure some of these are common sense to some, but they make difference, and in 2s (lol @ afflock in 2s) every little bit helps.