These are the ones I've encountered no issues with.
BM hunter. Havoc DH. Blood DK. Ret Paladin. Moonkin.
Lock wasn't too bad, but the lack of instant casts is frustrating. It's basically a BM hunter but you can't move. Or interrupt.
Shadow priest was by far the worst class going undergeared at 120. Squishy as shit.
Shaman was alright. Lots of cooldowns to power though any accidents including the mighty Heroism.