I've been through MrT as a DPS (warlock, for whom that instance sucks. Never have I seen so many humanoid mobs immune to seduce! Let's just make warlocks next to useless in there as a CC class!) and as a tank (Rawr). Each time, the healers have been a paladin or a shaman (iirc). No HoT's. No group heals (besides chain heal).
Last night we went in with Posolutely, Byouki, Isabeaux, Neshura and Kiljara.
The pulls before the first boss... it's damn hard to keep the AoEing clothies alive, even with shield and flash heal. So, no matter what type of healer you are, be prepared to lose someone if they're AoEing.
If you're an AoE'er, try to give the tank time to build some threat before you open up, and be prepared to die.
Otherwise, prayer of healing makes healing in MrT... surprisingly simple.
The AoE damage from the first boss... cake. Just start casting your prayer before the first wave of damage comes in, and you're just peachy keen and fine.
The energy boss... same deal. Prayer of Healing = Easy Mode.
Priestess Delrissa was a bit tougher, but again, made relatively easy since I could heal the multiple people taking damage from their assigned mobs and the 'mini-bosses' random aggro tables.
As for Kael'thas... Boon always complains that he can't keep everyone alive. He can't cast because he has to move. People are constantly taking damage. And he loses people.
Well, he sucks and I rule because Renew = Love. Our tank was all 'Don't heal me, K!', and I was all 'Don't tell me what to do, gnome! RENEW!'. And no one died.
I attribute it entirely to my skills, and it has nothing to do with the overpowered DPS or tank (or the nerf), since the first time we went through it was with overpowered DPS and tank and healer.
So, it's all me, naturally. Priest = Best Healer Evar.
No, really. I think they are. Don't get me wrong, each healing class has their benefits. Paladins = Great Single Target healers. Druids = HoT masters. Shaman = Multi-task much?. Priest = Best overall all-around healer.
You can feel free to disagree with me, (but that would make you silly and wrong! ;) and if you do, please don't hesitate to share!