1) Final Fantasy IX
It is not only my favorite Final Fantasy, it is my favorite game ever. I love the characters, I love the story, I love the world.

2) Final Fantasy VIII
I think Squall is the best FF hero, I like most of the characters, I love the story, the world has some great locations, I love how involved the summoning is, I like the junction system.

(Here is where I would throw in Tactics and X-2 but you said no spin-offs)

3) Final Fantasy X
I appreciate Yuna more and more as I play, it's a good world, and it has some fun aspects to it. I do enjoy the story.

4) Final Fantasy XII
I like how open the world is, I like a lot of the characters, and the license board is amazing for me.

5) Final Fantasy V
It isn't the most involving story, but I enjoy the characters and the job system.

6) Final Fantasy VI
Strong cast of characters and I like the Espers that teach magic.

7) Final Fantasy IV
I haven't played much of this yet, but my impression so far is that it will beat out VI and maybe even V.

8) Final Fantasy II
Good game but nothing amazing.

9) Final Fantasy VII
I like some aspects of VII but there is a lot I dislike. The sense of humor is a bit crude for my tastes, I like very few of the characters, other than a few key locations, the world is forgettable to me. I like the materia system but I dislike how dependent it is on weapons.

10) Final Fantasy I
Good game, but still just starting so its lacking in a lot of personality and depth.

11) Final Fantasy III
I enjoy playing it but it is entirely too forgettable to me. I barely remember any of it.

12) Final Fantasy XIII
I enjoy playing it when I'm in the right mood, but overall has more negatives than positives.

13) 14) Final Fantasy XI & XIV
I haven't played them!