Jan, no question. Nalia has terrible thief skills, having dualled over to being a mage. By contrast, Jan is a multiclass thief/mage. I'd say he's the best thief in the game, and his mage skills make him an effective second string caster. When he gets to ToB, he really takes off, since he can learn all mage spells, and can get the skill to use any item.
To the Righteous belong the fruits of violent victory. The rest of us will have to settle for warm friends, warm lovers, and a wink from a quietly supportive universe.