Shaman with healing totem and wave....or the tree...freaking druid trees.
The only issue with creating yourself as one is the inconvenience of not being able to use the special abilities wynne possesses.
But being able to heal will allow you to temporarily bypass the circle of magi for now. (since you will be trapped there until you beat uldred. )
Depending on your spell choices, solo battles will be hard.
Double yourself as a blood/spirit. It does justice on nightmare. Granted that you have a good tank. (lol my dwarf tank had 100% magic resistance) So i could cast right on top of him and have him not take damage.
Of course Spirit healer/warrior, works nicely since you wear armor. However...too much is bad thing. Unless you know how to get around it. XD
If you can avoid the 1v1 logreghn...uh right i dont remember how to spell his name. Hero of the river dane. w/e. Oh and do not be the one to go into the kid's mind through the fade. Nightmare kills you as a blood/spirit.
also note that you will need to control your other players just incase they are not set up to target the tanks enemy. Often, if you are not careful, you will grab the enemies aggro...which means unnecessary healing.