At 9-1, I think I can definitely say that Warlock is crazy in Arena right now. Voidcaller is just SUCH a bonkers card, and Warlock also gets one of the better Lackey generators to back it up. They've nabbed a powerful board clear with Felfire Potion, and my one loss was to a Zoolock running a Darkshire Councilman + Lackey package that very quickly ran my more controlling deck over.

Oh, and the Old Gods are available in Arena at the moment, meaning that you can have N'Zoth generate a full board of Voidcallers after you've fought them to a standstill. I think C'thun and his related cards are still banned though.