most valuable is priest, at least on hard. we can contemplate any number o' party configurations, but on hard difficulty, we would not survive for very long w/o a priest.
am suspecting that with new build we we will need consider moving paladins up our list o' party mvp candidates... or perhaps not. in the most recent build, paladins were very easy to min/max into uberness and their buffs were some o' the best available in the game. however, while paladin buffs will become relatively even more useful, the removal o' accuracy padding from max perception will likely significant diminish their combat efficacy. currently, chanters is likely our #2 mvp behind priests. the buffing for chanters is excellent, but more significant is their summons. in a game with few party summons available, and a tendency for enemies to bum rush our little band o' heroes, summons is invaluable. in hard-mode, many enemies is capable o' one-shot or two-shot killing any party member, even our tanks. a summons that provides cannon fodder is welcome.
regardless, priests is clear #1 mvp.
HA! Good Fun!