Never use...

*Umaro- Just don't like him. Sometimes I name him Assrag.
*Gau- Never got into that whole monster ability thing.
*Strago- Never got into that whole blue magic thing.
*Relm- Just didn't want to use her. To many good enough characters already.

I use often...

Locke- Just do, no real reason.
Sabin- Blitz and I give him good magic.
Edgar- Tools and I give him good magic.
Terra- Magic.
Gogo- Having Blitz, Tools, Mimic, and Magic is awesome.

Runner ups...

Shadow: Fun to use sometimes.
Mog: Moogle Charm when I am lazy.
Cyan: When I am sick of Blitz and Tools.
Setzer: The slot thing is fun to me. Also, he is a back up magic dude.