Here's my top 5;
FFVI, FFIV OR FFIX (they go back an forth depending on my mood), FFVII, FFX
FFI, FFII and FFIII have not aged well. FFV is good, but I'm not a fan of the job system. FFVIII is a massively disappointing follow-up to FFVII, but I can tolerate it once I get about halfway through (I utilize a strategy that by-passes a lot of the drawing and functioning).
I don't count FFXI or FFXIV because they're MMOs.
FFXII has a great story, but I can't stand the gameplay. Zodiac edition might fix that, but I'm not holding my breath.
There really isn't anything good to say about FFXIII. I haven't played the sequels, which I have been told are better, but that is a small hurdle to jump