On the DS port, the hidden job Onion Knight. Before Onion Knight, you've got a wide assortment of different jobs with pros and cons. Granted, some are direct upgrades to others, but you've got a reason for a diverse party. After Onion Knight, the only reason not to do the work for four fully equipped Onion Knights is some artificial handicap.

On the original NES version I've only played as a ROM, my votes are Sage and Ninja for the same reason. They've been balanced in the DS port at least. I don't like classes that are clearly intended to be the final stop. I'd prefer a more egalitarian system.