Warrior, Mage, or Paladin?

I'm playing as a mage, and the main trick here is to focus entirely on intelligence and mana, without investing in defense or leadership, although the latter looks very appealing. Ultimately, if you overinvest in leadership, you won't end up as a mage or a paladin, but as some strange creature with zero chance of defeating Karador. I messed up my first playthrough because of this.