1) FFVI: Simply the best of the entire series, the story is very strong, the cast is amazing, and the visuals are just stunning. It's the series high point and one of the most iconic games ever made.
2) FFVII: While there are some drawbacks to FFVII (mainly bug issues, some bad translation, the plot at times can be hard to follow) in the end the depth of the characters, plot, and amazing detail of the world makes up for all of those things.
3) FFVIII: Many people hate FFVIII, and i think it's simply cause they don't understand the plot and the strong ties of fate that are being shown. The atmosphere is amazing, and the junction system is the best development system in the entire series.
4) FFIV: A Big leap from the NES days, FFIV has a wonderful cast and great story, it's really the first FF to really get everything right.
5) FFIX: The biggest draw for FFIX is the atmosphere, it really succeeds in recapturing the feel of the earlier games in the series will still providing a strong cast and story.
6) FFV: The job system really makes this a great game, the story isn't the strongest and the characters aren't either, but it's just really fun to play.
7) FFX: I've never been a huge fan of the characters or story of FFX, i find them annoying and dull, however visually it's amazingly beautiful and the combat is very deep.
8) FFII: The storyline is obviously not very deep (it's an NES game after all) but it was a big step up from FF and it really set the foundation for what the FF series would become.
9) FFXII: beautiful game, very expansive but the combat and story we're a big letdown, gambits took away from what FF should be.
10) FFIII: The last of the NES FF's i just never could enjoy it very much, it's to much like the games before it and failed to really take the next step.
11) FF: It's a good old time RPG, but there really is no story and it's pretty much just a constant grind. for it's time great, but it hasn't aged well.
12) FFXI: it's not even FF.