I think the worst characters were:

Rinoa: She was SO gosh darn annoying! Everything always happened to her. Plus her personality was annoying.

Cait Sith: He was annoying. I never even used him in FFVII unless I was forced to.

Seymour: He's cool (You have to amit that) but he annoyed the heck out of me. In my opinion, he was the worst FF villian because he popped up everywhere and then you had to fight him FOUR freaken times.

Selphie: Once again, another annoying person. The only good thing about her was her limit break.

I believe that's it...everyone else was ok.