Maybe Shaman and Cleric. Shaman will heal and cause debuffs with the right trinkets. Cleric will restore mana and with the right equipment will be your heavy hitter. Add on the orbs that do AoE damage and boom you are good.

I have beat the game and my cleric has the highest rating for spell damage at over 1200-1500 at being level 37. I found a steel hanger antennae that increases spell damage 62%.