for white mages their strength is in these spells.holy and vuraga and stuff like reflect
and stuff like that that can be cast ont eh whole party.
BMs have all the power and can cast flare and level 3 magic and in FF4 they can cast meteo.
TMs have good spells like comet and haste2(this is on FF5.)they also have the ultimate magic meteo "drools".
RMs.are good because they can equip good stuff and learn most spells. in FF5 he can learn every spell as long as it a BM or WM spell and has redX2 ability which casts twice so i think youll forgive his lack of HP when he casts flare on an enemy followed directly by a cure 3 on the party.(or somethin like that.)
blue mages are realy good because they have plenty of hp and can equip all of the decent stuff and some of the blue mage spells are sometimes amazing.
green mages are actually the little green old guys you find in FF5 towns and tey are teh coolest!!!