I used the Fang (as the leader because she's the best at dodging attacks), Lightning, Hope combination because it gave you the sentinel, synergist, saboteur, as well as two characters with the medic ability (that and I think Bahamut did a decent amount of damage). I started the fight using the synergist, saboteur, medic combination, it speeds you up and slows him down
Also if you don't have your weapons and armor leveled up you might work on that. I think I had both at their maximum levels, and it was still a hard fight.
Any other advice would be the same you'd find online in a walkthrough, attack the armor first (each piece has a weakness), switch to a paradigm with all three attacking as much as possible, and have combat clinic at the ready for when he does his best to blow you away
Good luck

, that was probably my least favorite fight of the game
