I'm going with five party members.

Rydia (FF4) - She casts the spells that make you go boom.

Faris (FF5) - The way I played her, she was the power house of the game. Until everyone started learning everything xD.

Edgar (FF6) - Dual weild Ultima Weapons. Also he has a chainsaw.

Yuffie (FF7) - She's fast and hyperactive. AND also to spite at you Yuffie haters.

Selphie (FF8) - Well, someone has to pilot the vehicles. Also I gave her most of the healing magic.