I think the best party is

Fighter, Red Mage, Red Mage, Monk

- can use the top 3 best weapons in game
- nice resistance
-awesome damages
- can heal pretty well
- can have low level class change
- can stack temper and haste on monk for 1-3 turn kill on any boss
- doesnt need AOE spells cuz they can sweep any monster with melee
- they "can" use black mage