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.
The Book of Ghost Crab:
And he led them out until [they were] over against Orgrimmar: and he lifted up his hands, and buffed their classes. And it came to pass, while he buffed their classes, he parted from them, and was carried up into the Emerald Dream. And they worshipped him, and returned to the General Forums with great joy.
Easy poll for me. Only have my Warrior which i made 8 years ago. Never had any alts.