Enhance Shaman since day 1. Shaman all the way.
While I've spent more game time on my druid over the years than any other character, I've had my priest almost as long and she's been my main for the most recent chunk of time that I've played. I love to heal, I don't tank, and I don't mind dps but I'm not very good at it, so if I was going to choose anything it'd make sense that I'd go with the one class that has two different healing specs so that if one gets nerfed to the ground (which might very well happen soon) then I'll still have the other one to play.
Therefore, I chose priest in your poll.
I'll tell you what I wouldn't. Melee. They're all mind numbingly boring in MoP. Attack, gcd, attack, gcd, check secondary power, attack, gcd, finisher. Repeat.
"I quit WoW."
Easy poll for me. Only have my Warrior which i made 8 years ago. Never had any alts.