Errr...
-Fighters are easy to use, fairly easy to level, and highest attack and defense...
-Clerics can heal and solo monsters many levels higher than them,but level sorta slow if you dont party
-Archers can give diseases and poisons to monsters and can aoe(area of effect)
-Mages do lots of damage,aoe, and have interesting skills, but you may find yourself dying
ALOT
Hope that helped