Tanks: Vaan and Ashe. Swords and shields. Heavy armours. Some buff magic and healing spells.
DDs: Basch and Balthier. Katanas, Spears, that sort of thing. Heavy armour. Some buffs.
Mages: Fran and Penelo. Bows/Guns. Primarily healing.

My Gambits were set up in amazing ways, but unfortunately I can't remember what they were. In 12, Gambits mean almost as much as good equipment.

EDIT: I found it funny that Vermachtnis' First Row and Vanguard are the exact opposite as mine! Vaan, Basch and Fran FTW!