8 was the worst one. Static characters, boring story, and I just hated everything about it. I guess the gunsword was cool, but for like 2 hours =/.
I hated 1 through 3, didn't play 4, 5 was one of the best and so much possibilities, 6 is one I barely remember since I played it at a friends house which I went over very little, 7 is the best to me in combination with ff7 crisis core, Dirge of cerberes is a game I never played but i heard was ok. 8 was the worst and 9 followed that theme... I'm sorry for any fans out there for those, but that is my opinion. 10 was a great game and I enjoyed everything about it, but they ruined it with 10-2 even though they brought the job system back which made me happy. 11, the mmo, has nothing or even anything remotely close to the FF series so thats just something I played for 3 years. 12 I didn't really like since I didn't care for half of the characters making me dislike playing the game. Friend helped me beat it since I couldn't stand some of the voice acting as well. I hope 13 is great... and 14, the new ff mmo, is something i've been waiting for. Beta in 4 months :O