I don't like to use more than one from each class. Because I'm picky like that. I use,

Fighter, White Mage, Red Mage, Black Belt

Fighter slashes people with his immense swords, and sometimes throws items at his teammates in need.
White Mage heals people, and occasionally attempts to beat people with his hammer.....you know.....when there's nothing else to do.
Red Mage does a little healing, but mainly manages Black Magic.
Black Belt destroys people with his ultimate fist attacks. Thats all he does. I'm pretty sure the only thing Black Belt knows is killing.