Aside from the rules, I say Crisis Core, but within the rules, I say FF9 for obvious reasons. HE HAD A TAIL!
I pretty much have the entire FF collection... <__> FF IX has some of my favourite game music though. They all have crackin' pieces but IX sticks in my mind, that n' X.
Breaking rules, I say VII. Mainly because it was my first one and it was very epic, so that set a trend for me to judge by. Following the rules, IX hands down. It has such a vast story and extensive side-quests. The music was lovely and Zidane and Dagger are just a giant emotional roller coaster.