"Hey, what jobs are you using?"
Thanks for asking! My goal going in was to use each job once, which is exactly possible with 12 jobs and 6 characters. I did a good amount of theorycrafting ahead of having them available to me, but through a combination of misunderstanding mechanics (e.g. a bonus that exists on both boards does not get doubled) and not realizing which jobs are way better than others, they ended up fairly uneven.
Vaan: Time Battlemage/Shikari
Time Battlemage is the only job that gives access to Haste (although Machinist can learn Hastega eventually), and for that reason alone, it's pretty decent. Access to Raise is also huge. Shikari gives some good damage options with daggers and ninja swords.
Rating: A-
Balthier: Knight/Foebreaker
This is a real flop. Knight and Foebreaker fill the same general role (heavy armor, big weapons). Foebreaker feels like the clear candidate for worst job in the game: it brings nothing to the table that can't be found on at least two other jobs aside from the axe/hammer weapon family -- which is a clear candidate for worst weapons in the game thanks to its damage variance. Foebreaker is also the only job to learn no magic. The biggest issue for Balthier, though, is that there's just too much overlap between these jobs. Foebreaker needed to be on someone who wants access to heavy armor and a pile of technicks, and Knight needed to be paired with something that offered more healing. He's the only character without access to Raise.
Rating: C
Fran: Red Battlemage/Bushi
I'm in a slump with Fran right now. Red Battlemage peaks early, before you get the high-end magicks it can't access, and Bushi peaks late, after you get the nicer katanas and some Genji Gloves. Effectively, Fran is acting as a poor man's White Mage at the moment, although I'm sitting outside the Gilgamesh fight right now. Worth mentioning: Red Battlemage has exclusive access to Death, which is actually a really great spell, just not one I'm going to put on a gambit very often.
Rating: B (with aspirations to become an A)
Basch: Monk/Uhlan
I'll be honest: I have no clue how well Basch really operates, because I slapped the Berserker Bracers on him ASAP and never took them off. Monk gets access to some high-level White Magic (Raise, Arise, Renew, Bravery, Curaja) that is otherwise exclusive to White Mage, so I will probably change this eventually (and the more I think about it, the more I think Balthier should be in this role). There's a case to be made that Monk and Uhlan are a little too similar, but in this case, I don't mind it: spears and poles are fairly interchangeable, so doubling up just means I get more regular weapon upgrades.
Rating: B+ (the B is for berserk)
Ashe: White Mage/Machinist
White Mage is frankly indispensable. You could maybe sub in Monk once you've got those higher spells, but you need a healer, and White Mage is very good at it. Machinist is a great sub for Ashe: staves don't really provide much in the way of bonuses (and White Mage doesn't need extra magic power), and guns are a good source of stat-independent damage that also allow her to stay out of the fray.
Rating: S
Penelo: Black Mage/Archer
Black Mage is basically always good. With the Sage Ring halving MP costs, you can sling Bio or -agas across an entire dungeon without needing a break. In the original release, black magic falls off late as you have to deal with the effects queue. I'm not sure to what degree Zodiac Age fixes this, but it at least seems less bad so far. Archer notably adds Raise and a third Swiftness, but for the most part, I think I could swap Archer for Balthier's Foebreaker (which also has Swiftness) and be in a better spot all around.
Rating: A+