Teh new mission mode is awsome (i thinki heard someone just yesterday saying misions would rock. Well, this is to you ;D ), but two maintenances in a row is real harsh.
Best path is mage. On defense quests, it's both ranged, and allows to stop enemies (with your body) and damage them at the same time. On dungeons, the regular atack increases your mana lore, aming your spells better (you realy notice the change when you do the campaign with any of the others).