The best party is a well rounded one.

Fighter, Blk Blt, B Mage, W Mage

But you can replace the BB with a Thief and still fare pretty well.

But keep in mind that at lvl 40 or so, the Master (BB after Bahamut) can hit around 20 times in one shot, even more when hasted. Seriously, he hits for about 800 or so on most monsters. Just don't give him a weapon. He's way more powerful with just his hands.

Feion