Tera: This spreadsheet simply offers the lowest/highest ranks for each of the spells grouped based on their use/behavior. This is not a level-by-level comparison; simply a general look at the overall healing skills to offer a comparison, though max levels are easily compared. It would seem here that Priests would be the clear winner in terms of overall ease of use.
Not only do they not require the party members to pick up the big direct Essence of Rejuvenation heals like the Mystic does, but they also get an AOE HOT and a very strong, instant self-heal(Tera Gold).
Mystics have to drop an orb for themselves. Also, Priests have a 15 MINUTE HOT buff for the party which does have an increased rank later on and seems to heal better than the Mystic's Sanctuary of Leech, especially since Sanctuary of Leech costs MP(buy tera gold) to maintain and fully requires the healed target to actively be doing damage(Tera online Gold).