Either go for a Kensai/Mage, a Monk or a Sorcerer; I think the easiest characters to solo with in BG2, especially with an experience cap remover. They will all have their difficulties early on in the game, but once you've gone past a certain point, you'll have an unstoppable killing machine at your disposal. Though if you want to keep it somewhat of a challenge, don't install the experience cap remover at all.
