OK I have to know so which one is it?  

VI. The only thing that could make it better would be if they put it on the DS, this included. DO IT, SQUARE! NOW!!!!!

8, though 6 and 10 are both high contenders as well.  

XII.

I've only played X, X-2 (barely), and XII. Out of those, I liked X the most.

The one that doesn't suck.  
 
 
 
Oh wait.

" The one that doesn't suck.     Oh wait. "

IX.  Fell apart towards the end, but I really enjoyed the characters and story,  an amazing celebration of all things Final Fantasy, with some really fun nods to all the past games.  I don't want to turn this into a debate about which games were good/bad, but I did really feel that all of them after this one went rapidly down hill.
 
I also really loved IV and VI.

Why on NES when GBA/DS Versions are far superior? 

Yeah!  X out in front so far. =P

" Why on NES when GBA/DS Versions are far superior?  "

Final Fantasy X.

7 is still my favourite. It's one of those games that I keep coming back to even 15 years later. Everything about it is great, oh except what the 7 fanboys have turned it into.

Final Fantasy X.I love that universe, characters, and story. 

FF9. The characters in that game were very anime-archetypesy. But it seemed justified due to the character design. That game had great sidequests and I loved the chocograph treasure hunts. Collectibles as well like the Stellazio coins, coffee beans for the hermit, and completing mognet. The game felt very complete. I also like the throwback to an actual 'fantasy' setting rather than this intricately designed futuristic crap that 7, 8, 9, and 10, and 13 have (nomura < amano). For the time, it was a very a good looking PS1 game (along with Chrono Cross). I liked FF7 a lot more than FF8, but when FF9 came out, that was my new "7." Everything after FF9 felt too different to be even final fantasy anymore.

VI (III).
XIII is fairly disappointing so far. I thought they were starting to go in the right direction with the steps towards non-linearity taken in FFXII, but so far, twelve hours in, I'm somehow already on the second disc (360 version, I know, I know), and all the zones are still practically straight lines.

IX all the way, bro.

I am shocked at the love 9 is getting.  I have it but I haven't played it yet.  I bought it a few years back when I picked up a PS1 for like $10 but the system looked like shit with the hookups included and the memory card wasn't exactly reliable so I put it into my game collection but haven't played it since.  Now that I have a PS3 it looks better and I feel more confident about the virtual memory card so I will be playing it next.  By the way 10 is my personal favorite but VI is pretty close.

X blew my mind

6 or 3 for me.

IX.
 
That game has mad heart.

IV (II on SNES) is the real answer here.

love number 1

VI 
  
Everything I love about the series.

FFX by far for me. I've played  FF4,7,8,9,10,X-2,11, and 12. Although technically you could never finish 11.

IV, I haven't played many FF games... or completed any, but I liked IV the most.

I have mad love for VII because it was my first RPG, but even so if I had to pick one I'd give it to IX.

VII. When I played it I thought it was the greatest game of all time. Haven't had another game impress me like that ever since.
 
 
I know I'm part of the problem.

My favourite is definitely VII. And I make no apologies for it, game was awesome in it's day and stands the test of time in my view. 

x was my first FF game, and it is by far my most favorite

10... blitzball is the greatest mini game of all time!

Xenogears!  oh wait...

X was the one that I remember most fondly of. Even though now that I look back, I cringe at some of the dialogues.

" X was the one that I remember most fondly of. Even though now that I look back, I cringe at some of the dialogues. "

when i think about it X stands out a lot to me

VI  (US III)
The best Final Fantasy ever, possibly the best RPG ever, Hell possibly the best game ever

I'm dissapointed Final Fantasy Tactics isn't an option. In my opinion that game had the most compelling blend of narrative and gameplay of any JRPG I have ever played.

7 or 8, probably 7.

II. I loved the system of using different skills to level those skills up. It just makes so much sense. 

Either 4 or 6.
 
I am not surprised at the love for 7, since it's probably the only one most people have ever played. (not saying this in a derogatory way, it's the truth).

VII
 
Followed by a tie of IX and X.
 
I like that FF XI doesn't exist.

" VII  Followed by a tie of IX and X.  I like that FF XI doesn't exist. "

I've only played a portion of 7, 8, and 10. Favorite would probably be 8... only because it's the only one I have nostalgia for.

I don't know why but I actually like 9 the best.

My favorite is 10