I honestly don't understand the Cait Sith answers.
Maybe for some of you he really is the most forgettable, and I know many don't like him as a party member.
But, like, if you can forgive a few
OPEN SPOILERS (for those of you who for some reason play many FFs but not 7)
I find it hard to forget the Shinra character? The scene where he gives Shinra the black materia was surprising for me at the time, especially knowing there was a spy, and then there's the whole Rufus scene where he shouts, "CLOUD! BARRETT! I'M SORRY!" near the end because apparently he's found out.
I dunno, for the purposes of the story, it's hard for me to forget him.
Or any of the 7 cast.
Caith Sith and Quina jumped in my mind first.
See what jumps in last and that's probably the answer. =P