I went with:

Vaan: Time Battlemage + Monk
Balthier: Machinist + Uhlan
Fran: Red Battlemage + Black Mage
Basch: Knight + Bushi
Ashe: Foebreaker + Archer
Penelo: Shikari + White Mage

Basch and Penelo ended up being the total MVPs, Shikari + White Mage is basically adding the passive role of tank to the active role of healer and works beautifully, even kept the Main Gauche (a dagger you get in Jahara) equipped until the end of the game. And as for Basch, Knights are already damn good on their own and Bushi gives them extra speed, magic power for their White Magicks, and the insane Excalibur + White Robes combo which completely tears through any postgame enemies that don't absorb or nullify Holy.

And the others were kinda there too I guess. Balthier was a good secondary damage dealer and flying enemy shredder, and Ashe had the absurd power spike of the early Vrscika which made her main damage dealer for a long time. Rarely ended up really using Vaan or Fran interestingly enough, despite how powerful black magic really is in this game.