As I have said in similar threads, I base my decision on which Job by their individual stats as a Freelancer.

In my current plathrough:

Bartz (Strength)- Monk, Thief

Lenna/Reina (Magic)- Black Mage, Summoner

Galuf (Stamina)- Monk, Berserker

Faris (Strength/Agility)- Knight, Ninja, Ranger, Mystic Knight