Mages are strong at the beginning of the game, up to around level 12-15, but after that, further increases in strength and knowledge characteristics become almost useless. For example, a hero with 12-12-5-5 characteristics will defeat a hero with 5-5-12-12, all other things being equal. The most useful combat spells are those that slow, bless, hasten, dispel, heal, and curse, as they don't require a large amount of mana. And most often, the battle lasts no more than 4 turns. In particular, in my opinion, the best hero is Sir Mullich - a warrior.