Zidane - Steal is very useful, so does Flee and he is also balanced. Dyne pwned your ass!
Vivi - Black Magic: Flare, Doomsday, Death, Osmose and Meteor pwned! I even equipped all Shadow-absorbing armor/accessories to my party so that Vivi becomes a healing machine with Doomsday. Double effect for Double Black Magic.
Eiko - White Magic: Curaga, Full-Life, Haste, Holy and Reflect, Summon: Carbuncle and Phoenix. Another healing machine! Perfect safe-play. Plus, I reflected Vivi with Reflect to trigger double damage. I even use Eiko when I have Auto-Regen equipped. SAFE-PLAY.
Steiner - Shock, Climhazzard and Darkside. And he can attack with Vivi! Fire! FIRE! FIIIIIIIIIRRRRRRRREEEEEEEEEEE!