6,12 and Tactics are my favorites.
5 is the runner up.
7 was kind of ruined for me after I read the FF House thing.
My shitty rundown of the series:
FF1 - had a fun time finally beating this game. Never played the ports.
FF2 - Love romancing saga but felt like a prototype for that series. Never got far. Excellent world map
theme.
FF3 - Haven't played.
FF4 - Really dug this game and I want to play the psp port with extra shit. The 3ds version's artstyle
makes me feel a bit sick.
FF5 - Kinda underrated but a lot of fun. Story is a bit sparse but quite a few silly moments. Felt legit
sad at several key moments.
FF6 - Best ratio between story and gameplay for me. My "lowest" favorite.
FF7 - Was a really charming game and I liked the materia system..just not as much as the espers
because you couldn't permanently manipulate your stats

.
FF8 - I really like triple triad and the junction system. Game isn't for everyone but I like it.
FF9 - Great game but coming out the same year as Chrono Cross and Breath of Fire IV my attention was
heavily diverted. The combat feels more shallow than previous games but I know there are some
neat little tricks I missed.
FF10 - Is a pretty solid game in spite of Tidus and the last boss being stupid and underwhelming.
This game gets too much hate.
FF11 - I missed this boat and regret it.
FF12 - I love this game a lot and don't even bother arguing with people who write out bullet points
about why its shit. Too bad about Matsuno's kickstarter

FF13 - I'll beat this one someday.
FF14 - Pretty good but I think I've outgrown mmorpgs. Sometimes I think of subbing back.
FF15 - I didn't beat this one but I had a lot of fun? Worst part was the load times but now its on steam so I can play on my SSD.
I never played: Revenant Wings, Tactics Advance, A2, FF3 and X-2. Never touched the FF7 extended universe shit. Crisis core looked cool. You could call me an FF fan I suppose.