The "again" is cause I'm certain its been done to death but due to the release of the PSP port I feel its time to re-evaluate the job classes. Now I have always been impressed with Tactics cause the job class system has always been fairly balanced overall, granted the PSP version kinda smurfs this up due to Dark Knights and Onion Knights being horribly overpowered but they are off-setted by both needing steep requirements in order to get access to them.
Regardless, this is a series where everyone has their favorite party combinations and lord knows a few of us disagree when people swear upon the uber-godliness of certain classes; but let's face it. Some classes are not nearly as good as people say they are.
My two choices are Calculators/Mathematicians and Ninjas. The first one has easily the worst stats of all the classes, yes their abilities are useful cause its instant casting with no mp cost but the work needed to make sure you don't nuke your own party or worse, heal and buff the enemy party is not worth the stress IMO.
Ninja's are another class I don't care for, weak weapons, lousy hp and defense making them glass cannons. Their only plus is their speed and an d a few abilities that once again are better served in other classes. Like the Cal/Math, I feel its a class you jump into so you can get a few useful abilities and then you never look back unless you need a real thief (unless you have Balthier then its not worth it).
An honorable mention goes to Summoners but luckily its easy to offset their weaknesses so its only a minor hassle...