7,8,9,10,12 I loved them all.
7 for obvious reasons great story one of the greatest villains of all time and great side quests.
8 despite squall being a douche. Really enjoyed had some great battles, a epic card game which led to such a monumental side quest.
9 was hit and miss but I really enjoyed it again the card game for me made it cool
10 I enjoyed the storyline a lot. Blitzball was great and the monster arena was awesome especially the stupidly hard battles from collecting all the creatures in certain areas. There was one in there that made the end boss look like child's play can't remember it's name.
12 a lot of people hated this but I enjoyed the chasing down of marks and didint mind the storyline too much yes I missed the turn based style combat but it still had a great amount of charm.
13. For me was so tedious and had no epic sidequests imo and I didn't like the combat system one iota.
All the early ones I have briefly played but have a poor memory and don't remember them well and haven't played them enough.