My favorite is Fighter, Black Belt, Red Mage, White Mage.

You never need more than two fighters, so it's not really worth it setting a third character as one. I never use the theif because their completely useless and I rarely use a black mage because they are pretty crappy too. I always take a white mage, if anything so I can cast exit after I get the Masamune in the last dungeon and go save it. Also because I never buy heal potions. I just use the cure spells.