I've only played 5 of 'em (4 out of the 5 are in my personal top 20 of favorite games)...
1. Final Fantasy VI - It has my favorite cast of characters from any RPG. Tons of memorable moments, a really good story and all of the sidequests that you can do at the World of Ruin really flesh out the characters. Also it has my favorite video game villain ever, Kefka.
2. Final Fantasy XII - Great world to explore. Balthier is my GOAT character and I liked most of the cast (though I wish Vaan and Penelo had been more fleshed out). Liked the political tone of the story. The hunts are great sidequests.
3. Final Fantasy IX - Finished this game for the first time a few hours ago and it was wonderful. An amazing experience with a lot of charm and great characters. One of my favorite endings in a game (if not my favorite). Spent so many hours in the Chocobo hot & cold mini-game...
4. Final Fantasy X - A lot of great memories from this one, I loved the battle system and the plot. It would be higher in my ranking if they had not removed the world map and the sense of exploration...
5. Final Fantasy VII - I liked it a lot too

IX and XII could switch places depending on my mood
I wish Hiroyuki Itou directed the next game after XV...

Op has terrible taste lol ranks FFV first lmao i get the feeling he only played that game once because i recently replayed it and....Yeeeeeah.

Anyhow id say.

1. FFIX
2. FFVII
3. FFVIII
4. FFX
5. FFVI
6. FFIV
7. FFXII
8. FFV
9. FF
10. FFXIII
11. FFII

I don't count online FF as mainline games sorry.

I wish I knew how long I played, but it was probably around 150 ish hours. Under rated game with a battle system that just keeps on getting better. The fight with Vercigetorix? was crazy. The plat grind at the end was not my favorite part. :)

I honestly thought op was trolling when i entered the thread lol either that or he's lying and has never really finished most FF's. FFIX is usually regarded the best FF amongst FF enthusiasts or at least top 3, its also the highest rated FF on the metacritic and was the creator of FFs true vision of how he wanted FF to be. 

Yeah I always thought IX represents everything that makes FF so great, that doesn't mean is perfect but it shocks me that some people may think is the worst of the 15

Bravely series gives me a real FFIX vibe actually. Ive always enjoyed the more "Fantasy" feeling of FFIX rather than most the others have more of a Sci-fi feeling.

1 - Final Fantasy VIII

2 - Final Fantasy VII

3 - Final Fantasy IX

4 - Final Fantasy XIII

5 - Final Fantasy XIV

6 - Final Fantasy X

7 - Final Fantasy VI

8 - Final Fantasy IV

9 - Final Fantasy XII

10 - Final Fantasy V

11 - Final Fantasy III

12 - Final Fantasy I

13 - Final Fantasy II

14 - Final Fantasy XI (FF XI it's at the last position because is the only one in the main series i didn't play and not cause i don't like it)

Vercingetorix wasn't that bad for me actually, I had a pretty good tactic against him and later came back to him to grind for platinum. But I had a real headache with Kaktorius. That sucker jsut kept on hitting me with 7777 hit points nonstop, I had no idea how to counter that. I mean I could go in full defense and survive until the end of time, but then there was the time limit to get gold for that mission! It was really hard. God, I hate Kaktorius. 

And yes, the battle system is very much underrated. It has so many options, it feels fluid and fun. I think most people just didn't play enough to fully get to know it, I can't explain it any other way. It's true that the start is kind of a stretch. But once you get a little further, the battle system is the best I have ever player in a JRPG. Period. Screw the haters! =D

Why do people ignore FF11 and FF14?
I love both of those MMOs.

Top 3 in no special order:

-FF XII
-FF IX
-FF V

The rest.