Necromancy. Because if you're going to cast spells then you might as well do it properly; i.e. as creepy evil wizard with gaunt flesh and a cowled robe, with a skull topped staff and undead minions. And nothing says "I'm a powerful mage" better than getting surrounded by enemies, saying a short phrase which drains the very life essence from your foe, healing yourself in the process and turning said foe (who should now be dead) into a mindless rotting slave...