A Mage isn't a bad choice at all, but a Mage with some combat skills (at least with defense and resistance) is even better. And you still need to find a Guard Robe somewhere. I'm just speaking for myself: I get defeated when huge armies clash, and if my hero doesn't have any combat skills. They can poison, attack, or cast a spell, and that's it. But if you can manage without combat skills, it means you're simply playing better than me, and honestly, I'm not a very good tactician (I'm talking about the fourth game). :)