First time through I just got everybody everything and used whatever seemed best/convenient. More recently I've tried to loosely fit the zodiac job system to my characters in the original version, blending role-playing "jobs" with the practical concern of who has a comparative advantage (to use a term from Economics 101) in a given weapon type or skill.

Role-playing wise, I blended my own vision of the character with others' visions, such as from Revenant Wings.

So I started with something like: Basch = knight, Ashe = time mage, Fran = archer, Balthier = sky pirate/machinist, Penelo = white mage, Vaan = ninja/thief

Then I add a second "zodiac job" that corresponds to weapons or skills that the character is relatively good at compared to the others from a purely statistical perspective. So Ashe += samurai (katanas) and Balthier += breaker (axes & hammers), then Vaan += black mage and Fran += red mage, since they are the next two most-powerful magic users after Penelo and Ashe, who are casters in their "primary" roles. That leaves Penelo += monk and Basch += dragoon/lancer