Priests imo. Paladins strike me more as "holy warriors" than healers, druids are so versatile in-game that its difficult to tell their 'true purpose,' though they are certainly healers, shaman commune with the elements, but none of the four Fire, Earth, Wind and Water are really directly related to healing *So much as the light, anyway. This leaves Priests are true believers of the light. holiness, healing in general, etc. And lolshadowspec.
Well, I think so anyway.