I'd say Black Magic. I've always gravitated towards Black Mages and their spells. Especially the Ice and Blizzard spells.

Least of all Green Magic. I get all exceted when I learn status buffs, but then I never use them, except occasionally haste. I usually prefer to spend a turn doing damage and healing instead of buffing, even though I am aware that it can turn the tides of a battle. I guess it just doesn't click with me.