Mage/disc is doing really well right now. You can roll up pretty high with some decent gear if you go arcane. Rogue teams will usually eat you alive though. There's a lot of very high teams that are frost/disc. This is a much better set up but requires you to have a mix of high end PvE gear mixed with good PvP gear. If you can pick up the deadly 5 peice and mix that with belt,boots,cuffs, wep, and offhand from naxx 25/ulduar then you should have the SP needed to take down holy pallys.
I've also had some success with arcane/resto sham. Once again rogue teams are a issue as well as DPS/lock teams. But you can breeze through ret/holy and holy/DK teams if you have a good shaman healer.
Mage/war is pretty fun for a while, but disc/DPS teams are sometimes a problem, especially disc/rogue (which is very common)
I'm sure there's many other teams that will do well. Just remember you'll be facing a lot of disc/DPS teams and holy pally/DPS teams, so try and find something that can counter those and your set.