Absolutely VI. Nothing else comes even close. It's not even my favorite FF, but the ending is just... wow.
Worst? Probably VII, but I can't be sure. I haven't played it in a while. Ironically enough, VII is one of my favorites, even ahead of VI.
Quem disse que a boca é tua?
Qual é, Dadinho...?
Dadinho é o caralho! Meu nome agora é Zé Pequeno!