I used to play all of the healers in Mists but since then I've moved back to my Restoration Shaman only.
Probably has the highest skill floor out of the healers due to heavy reliance on allies and very stressful situations that can cost you the game. A lot of what people have said about them in this thread is true, except that if you find a good Warrior you can play offensively in 2's. I've seen a few good players pull off offensive gameplay as a Restoration Shaman, you just need really good partners.