The number 1 strategy right now is probably mage while focussing on XP. The reason is, that it creates a snowball effect. The more "simple interests" you have, the more XP you get, meaning you can get even more the next turn.
You may think, you get more experience but in return for that you do less damage. But that's not true, because due to the more experience, you can easily catch up the damage. And, where it becomes really good, is when you have the ability that means level ups increase damage. If you have the ability where each level up increases damage by 1, and you have 8 simple interests at the start, then you get a default +8 damage.