Depends on what you're fighting. Against massive numbers of aggressive, low-damage melee mobs (not counting slimes, which are very annoying for melee), whirlwinding sampires are ridiculously good AoErs. Witherers are good for aggressive mobs that you can out-maneuver. Spellweavers (Essence of Wind) are outstanding for spread-out mobs and non-aggressives -- the range of essence of wind with a level 6 focus is literally the entire screen plus a couple of tiles in every direction. It's lower damage than wither though and a slow casting time. You can combine weaving & necro for a good package.
Final alternative: mysticism. Hail storm is slower cast than wither but faster cast than Essence of Wind, and higher damage than either. It's not quite as high-damage as a sampire with whirlwind, but for a caster I think it might be the new way to go AoE-wise.
For the lazy (like me), taming makes AoEing easy -- just invis and let all the mobs crowd around your GD, then cut loose with whatever spell you're using. Granted, taming AoE templates are *very* tight.
