Assuming we're talking about MMOs, generally priest or whatever is closest to a "pure" support character. Different games have different ideas about what that means or what the priest's place should be though. I love playing the support character when they're linchpin holding the party together in a variety of ways, always with 10 different things they "need" to do at any given time.
Priest in RO was a lot like that. Priests could gear to be almost as good at tanking as "real" tanks, so they'd often be tanking as many monsters as they could without dying while also worrying about keeping everyone alive, resing those who died, keeping buffs active, curing status ailments like stun, and casting a ton of different situational spells as needed. (RO was great about that: there was a spell that halved cast time, one that doubled damage to a target enemy, one that blocked all ranged attacks, one that blocked a certain number of melee attacks [and these two could not be cast near each other, so postioning them was huge--a bad range-block making an essential melee-block uncastable, or vice versa, could be an instant wipe.]) Almost all these spells were insta-cast, but they had varying aftercast delays, so you were always juggling whether it was safe/appropriate to cast Spell X--it'd be instant, but you might not be able to cast the far more important Spell Y in time, thus ruining everything. (In some dungeons and PVP situations, support scholar was also incredibly fun in a similar "omg I have a billion things to do and keep track of at the same time" way.)
But like, priest in WoW never appealed to me. I did like warlock though--DPS one mob while seducing a second while chain-fearing a third but managing its position so it didn't pull adds. Though WoW was a far simpler game in that there was a lot less to it and eventually add-ons automated away even the most trivial "I actually have to pay attention" parts of it.
I don't like priests if they're one-trick ponies that just heal and don't have much else to do, or if they're semi-support classes that have a few "nice but not essential" spells and are otherwise DPS. In any new game, I always start by making a priest, seeing how it's like, then if it's one of those categories, reading about the game and just rolling whatever class seems the most overpowered. (Hello sorc in RO2. It got nerfed into the ground some time after I quit, but when I played, with the right build/gear, it was the best soloist in the game and a better healer than a priest and a better DPS than a wizard.)
