Against the final marks, I found myself just using trios of all classes (COM+COM+COM, RAV+RAV+RAV, ...). Doing that just gets the job done so much faster. As for characters, Fang is a must for me. She's the best character in terms of damage and only her and Vanille can cast the really good Synergist spells. For comparison: Protect increases defense by 33%, Protectra by 50% - Bravery increases physical damage by 40%, Bravera by 80%. I also usually had Lightning because she is well-balanced, good at everything but Medic, great at Ravager. Lastly, I had Sazh at first because he's awesome, but when I found out how bad he was at fighting I switched to Hope/Vanille because one really good Medic is almost mandatory.