Wiz is probably best at PV because of spark -> DB -> expel. Psy coming second with spark -> physical immunity -> nuke -> stun after immunity -> nuke more.
Pk: solo psy for sure, in party wiz and psy are very evenly matched. Ninja you're forgetting the psy sage ability for aoe purify, the aoe stun, the ability to stop APSers with a soulburn, chan decrease on casters. Or simply switching to white voodoo and becoming a barb for a while.
Cleric/mystic are extremely usefull as support too though, just not nearly as good solo. Wiz is pretty good solo as well with it's stun/seal/sleep abilities as well as defensive slides & good pdef.
Party depends on party for what. PVE I'd say veno for the debuffs, pvp any of them rock.
Boring: depends on the person playing it.