In Final Fantasy

I always beat the game with 2 fighters, a black, and a white mage.
After beating it I always try to throw a ninja, thief, or red mage in the mix, but can never find the right combo.
Now, I have read the guides on how to beat the game with 4 red mages, but I am looking for the most effective team that includes one of them (ninja, thief, red).
I am presuming that it would be most easily done by replacing a fighter with one of them. But want to know what you all have to say.

Also, which character becomes the best after talking to Bahamut and 'growing up'?

I always use the Fighter, Red, White, Black Mage line-up. It's always worked for me.

As for the Bahamut scene, I'd say that the Thief becomes pretty cool after the event. As for most POWerful... I'm not really sure.