I actually liked Cait sith O.o I don't know what I did differently, but he was pretty strong in my team.
Well... until closer to the end, then everyone else sort of shot past him.
But before that, I loved him for his high HP level. Plus, I just like his character. People who are yelling 'what is the point' of him... doesn't the Black Materia ring any bells?
All in all, my worst characters were Aeris and Tifa. Aeris was great in the healing part of course, but then goes and gets all deaded so great help to me.
And Tifa just sucked.