I have 2 teams:
Basch tank / healing w/ potions, Balthier ranged (bow) / heals with magick, Vaan mage / thief

Ashe tank / healing w/ potions, Fran ranged (bow) / heals with technique, Penelo techniques / thief

This way I always have MP for quickenings and summons on my B team, in case the A team sucks at a boss / fiend.