Ninjas are only really great for their Two Sword ability. Once I get that, I just use it for other jobs. Their "Throw" command is silly. It doesn't do nearly enough damage. It's good for situations when an enemy is almost dead but you can't reach him with a regular attack, but there are other skills that would be better.

I had a friend who LOVED Samurais, and I don't know why. They don't do much physical damage and they can't use shields. Their draw out skill isn't good except for a few of them (I like that one that does Protect and Shell, and the one that heals allies).

And, finally, Lancers. Their "Jump" skill is too unpredictable. You can never know if your target is gonna go before you land until after you decide to jump. You can use the CT gauge to determine, but it's not set in stone. Also, they do less damage than other physical classes. And Jump doesn't get useful until the later skills, which are kind of pricey.