FFVI was definitely the one that got me the most... I played that game through at least 20 times, although I also liked IV... it had a few of the best characters IMO (Kain and Rydia). I'll be honest though, I was a diehard Nintendo fanboy back in the day, and when FFVII was released on playstation I boycotted it...
It wasn't until FFXI was announced that I finally broke down and bought a PS2.... and decided to buy the FF library for PS1&PS2. I liked 7, but wasn't as blown away by it as others were... I hated 8 (not really sure why to be honest, but just couldn't get into it).... then I played ...9 and played it again... and again... not sure why I liked it so much... maybe it was the story, maybe it was the humor, it just clicked with me and I truely enjoyed it.
I never finished 10 (I found it far too cinematic for my taste... and thus never played 10-2), played 11 for more years that I care to admit (Beta through to the end of last year) and dabled a bit in XII and XIII (I really like XII, but never had the time to really sit down and enjoy it... XIII made me angry after about 8 hours of straight line style play). I recently bought XIII-2 just because it was somehting like $10 lol, but haven't loaded it up yet, as I want to finish XIII first to see how it ends.
Loved FFVI and FFIX, played the snot out of FFXI and currently enjoying FFXIV and hoping for good things with v2.0
95THF, 95DRG, 90BRD, 94BLM, 95BLU, 90COR - Retired: Nov 2011
Someday soon my friends, this ride will come to and end, and we can't just get in line again.