Zidane is probably one of my favourite main characters from FF, but that's more from the fact that FFIX was the first FF I played than anything else, and I feel as if the games been with me for years.
While I thoroughly enjoyed XIII and it's cast (even Hope) I have to admit FFX had a great cast. Not perfect by any stretch of the imagination but the only character who annoyed me was Tidus at the start and that was sort of the point. Which they'd shown more of some characters though.
I've just actually finished FFX btw, loved the game but the whole ultimate weapons thing sort of left a sour taste in my mouth since I really don't want to spend 8 hours playing blitzball or lose the plot trying to dodge 200 lightning bolts... and don't get me started on the chocobo racing.
I never really said IX had the best cast, just my favourite. I haven't played enough of IV but V? I always felt the characters and story were the weak point of the game. Not a terrible game by any means but still...