Once you get Fang's Saboteur skills up, Lightning/Hope/Fang should easily be the best party. All the bases are covered in that group. Hope can buff, damage, and heal, Fang can damage, tank, and debuff, and Lightning can damage and backup heal if you're in a bind. If you use Snow, you'll have to replace either Lightning and perhaps get a small boost in damage but lose an extra medic, or replace Fang and lose a Saboteur. Not worth it imo. Right now my Lightning and Snow are almost equal in Strength, but I'm in ch.11 so maybe he gets stronger.
But I'm still using Vanille because I don't like Hope.

In the end it probably doesn't matter much, most group combinations should be able to get through the game just fine. Lightning/Hope/Fang just looks to be the optimal setup.
Oh, and protip: if your controller battery dies in the middle of a fight, the game doesn't pause. On the 360 version at least.
