Well the burn in period is over, and I've leveled both my priest and paladin to 85, and having done a few dungeons and heroics on each, I see a world of difference.
My priest is mana constrained, I struggle with throughput, and I have a heart attack every time a pull doesn't go perfectly.
My paladin finishes most pulls with 80% of his mana, I have no trouble keeping the whole group topped off, and I have a lot of tools to smooth out bad pulls, like divine protection, salv, etc. It's really so much better right now as a holy paladin then as a holy or disc priest, at least for me.
This is all 5-man, of course, I could see how holy priests could tear up raids, but right now I just can't even bring myself to log onto the priest right now. So I think I'm a paladin, for now.