No argument about Calculators as a class, although their Math Skills are one of the prizes in the game. There are plenty of ways to avoid self-damage, particularly with Holy. It's my secondary skill of choice.

The useless part of Ninjas for me is that most of the Throw commands go unused except for Throw Shuirken and Throw Ball. I'm not gonna hurl a spare Excalibur at my foes unless I'm in the endgame.

As much of a fan-favorite Cloud is, I find his Limit skill is hampered by the time limits placed upon them, not to mention weapon restriction. Even a Bard has more weapon options. Although Finish Touch has some nice status effects I usually have him use secondary Math Skills rather than go for a sword strike.

I also don't have much use for Geomancers. It's not that they can't do damage, but the status effects depend on terrain too much. I like having more control.