Summoner or Blue Mage. What can be more fun than having a big dragon torch yoru enemies with Megaflare? And blue mages are cool to do that annoting stuff monsters mostly do to you (Flash comes to mind, grr...). Revenge is a sweet thing.

Necromancers are fun too for their nice looking spells, but you get them so late in the game that I barely use them. A shame, really.