In my opinion
-A pure mage, who can cast any element
-A sword-and-board warrior
-A Pure Ranger
-One whatever you want.
For maximum OP, every character should have Leech and Glass Cannon.
Everyone should also put a single point in Witchcraft, and learn Bloodletting, which (with Leech) is a full heal spell.
After getting Glass Cannon, Constitution becomes more important than Speed.
Give your Mage leadership.
Make one character a Blacksmith / Crafter (I recommend Ranger)
Make one character a Barter / Charisma (I recommend Warrior)