I've played through the game once on the DS version, so I can't speak authoritively. An unfortunate drawback of the importance of class levels is that I didn't get to give all the classes a fair try, like in FFV.

GOOD:
Dragoon - Dragoons are my favorite FF class ever, so I was going to have one in the party weather they sucked or not. It actually turned out to be a very powerful and useful class. Though I virtually never had a use for jump Dragoons were itemized very strongly and consistently stayed near the top in damage, not to mention could keep themselves up with Blood Lance.

Red Mage - OP at the start of the game. (I think this is common knowledge). I ended up keeping a Red Mage in my party all the way to the last crystal, and because of the fact that her job level kept increasing she did damage on par or higher than my melee characters in most cases.

Dark Knight - Hurt by lack of armor selection for most of the game. Souleater was sucky when I first got the class, then became incredibly useful, then began to decline into uselessness by the time I got the the final crystal.

BAD:
Warrior - Kind of a disappointment that this class didn't do anything better than the Red Mage in any way.

Ranger - I only tried this out as soon as I got it, and it was terrible. Can't comment on scaling.

UGLY:
White Mage/Devout - Not much to say, did his job for the entire game.
Knight - A little underwhelming, the Knight just felt like the Dragoon but not as good.