1)Druid you want them since they top the healing parse (and ubba AoE heals)
2)Hpal since they make the best Mtank healers
3)Rshm get the best heals when your teamate are low on HP.
4)Priest ?
But what is the power of a priest ? Is it just because they can shield your tank ? or to replace the Rshm in heavy mobility fight ?