So it's been about 4 or 5 seasons since I've done competitive PVP on a warlock in Arena. Strangely enough, it still feels about the same strategy and playstyle that's required for an affliction warlock now as it did back then. I am seeing a lot of destro locks in arena too though. I gave that a try, and it's definitely not my cup of tea.
That said, destro is easier in arena for sure. At least in the early brackets. While I have yet to get there on my lock, I'm guessing that 1800+ is probably where the good locks will show up vs the bad locks leaning on destro to get them there. As for affliction, I'm enjoying it so far, and have been doing 2v2 with an insect swarm resto druid. We don't do a lot of games each week, but it's nice to get back on the old warlock saddle.
Also, look for another post later this week to see my warlock UI setup, along with the addons and macros I'm using on my lock.