For me VII first and I can't see that changing due to the fact that it was so far ahead of anything else in its day.
Surprisingly, I would go for IX next because it was altogether lighter in feel than the others (and I loved Vivi).
VIII is my third choice, I loved the 'feel' of the word and got addicted to Triple Triad.
X is a distant fourth. I still loved the game but I wasn't very keen on Spira as a game world and none of the characters absorbed me as much as the earlier titles (Auron being the exception).
Surprisingly, I would go for IX next because it was altogether lighter in feel than the others (and I loved Vivi).
VIII is my third choice, I loved the 'feel' of the word and got addicted to Triple Triad.
X is a distant fourth. I still loved the game but I wasn't very keen on Spira as a game world and none of the characters absorbed me as much as the earlier titles (Auron being the exception).