I tend to cringe when people extol their level >40 characters. It is not so bad when they are pureclassed, but some of the dualclassed and multiclassed characters are just plain... warped. The game is not designed for such high level characters, solo or not solo.
That said, my favourite character will be
Leonardo, my solo Cavalier. He maxed at level 34, and kicked butt all the way.
Next in line will be Odin Magnus, my solo Sorcerer, and the first soloist to complete the game on Insane Difficulty all the way to the end of ToB. He maxed at level 31.