I usually decide at the beginning what I want my team to look like.
Last game I had everyone focus on Nature. It can work. In fact the fighters have an HP advantage so they come out quite nicely. Only downside is when you get to some points in the game, nature doesn't have enough high damage spells and then its a long slow grind with auto healing. And the summons are never good enough. They look cool, but most of them are a waste.
Have done all other types of parties.
Mixed and balanced.
Full melee.
Full ranged.
Full Combat.
Half combat/nature.
Full nature is by far the toughest.
Others are OK cuz the potion system makes high damage groups easy to play.
If you like ranged but want the HP and armor of a melee, get a modification that adds throwing weapons like darts, axes, and bombs. You will have a powerful team if you focus.
www.moddb.com