I like Selphie myself i think her Full Cure limit break really helps out the party.
If you wanna talk useless characters then i would have to point at Quistis and Rinoa!
First Quistis blue magic is not that really good especially when you have guys that can do over 100.000 damage in a row with their limit breaks
The we have Miss Rinoa granted she can have a devastating limit break (Angel Wing) if you use Meteor atack what can she really do besides that?
At least Selphie works as a cheap healer.
My favorite party consistes of Irvine;Selphie and Zell.