I like 3, 4 and 5. Played a bit of 9 but didn't care for it too much.
I also like Tactics, Tactics Advance and Tactics Advance 2
As well as Chrystal Chronicles, CC: Echoes of Time and CC: Ring of Fates.
Final Fantasy IV was a good one, as was III and VI. I like the older ones that are open with side quests, kind of like a single player MMORPG. XIII wasn't all that appealing to me, I liked the battle system, but it was too linear, almost to a literal point, which pestered me immensely. I hope that gets fixed in XIII-2.
I wish XIV had been good. Is there still a console version in the works?