Enhancement, although I'm not 100% sure yet whether I'll play shammy or priest in WoD. I typically heal, but I prefer priest healing. However I absolutely love enhancement and absolutely hate shadow :/
First half of MoP I was pretty much maining a priest, then switched to shaman. This behavior has been quite typical to me in the past expansions :P I'd want to play both but I don't want to try keeping two chars raid viable and with my loot luck keeping even one is hard enough.
But if I'm a shaman, then it's enha and resto for me. Healing is probably what I mostly identify myself by, but when it comes to shaman, I love enhancement so much that for me it's like having two mainspecs. Resto healing isn't my favourite out of healers, but it's nice enough and since I love healing in general, it's still good anyways