Either one? Where did that come from? Anyway, I don't want to put research into a game. It just would prove I have no life. Read
http://dungeonfighter.nexon.net/Characters/Slayer.aspx that and tell me that those four classes don't sound a lot alike. One is good at swords, one is the same except he has poison and rage. The other two just like to spell cast, except one is blind. Fighter isn't much different either. The other three have unique sub-classes though.