Here's my go to team (at that time):
Lightening: Good Commando, Decent Ravager, Decent Medic.
Sazh: Good Synergist, Decent Ravager, Decent Commando
Vanille: Good Ravager, Good Medic, Good Saboteur
I tend to have two "attack paradigms" like: Com/Rav/Rav and Rav/Rav/Rav
I tend to have two "Stat Paradigms like: Com/Syn/Sab and Com/Rav/Sab
I always have two "heal Paradigms like: Med/Rav/Med and Com/Syn/Med
Kick things off with Com/Syn/Sab and get your team powered up while at the same time weakening Bartandalus. Once your teams "Magic" is boosted and the head of your choice is weak against "Magic", switch to Rav/Rav/Rav. Alternate between that paradigm and one of your "heal Paradims". Whenever your boosted stats wear off or Bartandalus' negative effects wear off, go back to using Com/Syn/Sab. Always try to keep your team's HP pretty high, too.
When Bartandalus tries to use his ultimate attack, summon your Eidolon to take the brunt of the attack. It'll only work once, though. Also, make sure that your party is wearing all of the HP boosting, damage absorbing equipment that you can. Strip anybody that's not going into battle of their accessories so that your battle party is sure to have all of the best items.
Later in the game, I found Hope to be a much better Synergist and Fang to be a much better Sabotuer but at that point, they were pretty underpowered. Later on, try using Two Synergists instead of One Syn and One Sab. Give two Sabs instead of one Syn and one Sab a shot, too.
AND MAKE SURE THAT YOU HAVE BATTLE SPEED SET ON THE SLOWEST SETTING FOR THIS BATTLE.
Good luck!!
