1. In what order did you level your healers from 85 to 90?
Mistweaver, Iritha, shaman, 2nd priest, paladin.
2. Which feels the most powerful?
haven't raided on the MW since late T14; felt more powerful on my shaman once I brought her in. I feel most powerful on my priests, even though shaman healing is also damn lovely atm. I've barely done anything on the paladin, on whom I've never done more than LFR, and even that not since 5.4 hit (too busy).
3. Which is the most fun?
Disc priest, shaman next.
4. Which healer would you be most likely to level another one of?
Priest, for tl;dr reasons... but shaman a close second.
5. Has your main changed since Cataclysm?
ugh, yes. This was my main through the last half of Wrath & all of Cata.
At the end of Cata I decided I'd go Mistweaver for MoP because we all knew it was going to be really strong and I figured it would bring versatility to my 10man raid (we were 2 priests & a resto druid in Cata). instead, the resto druid decided "someone has to be a disc priest" and went Disc so we had 2 priests anyway, plus MW didn't end up appealing to me.
So since the resto druid had already gone Disc, and I didn't feel we should 3-heal 10man with 3 priests (lol), I grabbed my shaman and finished T14 and all of T15 on her. She's still my main on my 10man server, but that guild... is on a lonnnnnnnng break from raiding now, so I transfered Iritha to another realm and am raiding on her now.
6. Which healer are you likely to play in Warlords of Draenor?
Iritha, and my shaman.