It was a hard choice between 6 and 7. Excellent graphics, excellent concept, excellent gameplay, excellent secrets, excellent feeling at both. Then I voted 7 for graphics.
Let's see the others I have played:
FFIV:
It had overall a good feeling until the middle of it. After a time, it got simply too hard. A bunch of high defense enemies striking first and then striking again plus draining HP? Oh, Square... Plus I couldn't stand some characters like Cecil, Rosa and that dragon boy. Rydia and the ninja guy were nice though.
FFVI:
Almost voted. Perfect, but not 3D.
FFVII:
Voted. Perfect AND 3D.
FFVIII:
It's a joke! I loved it at first gameplay, but after all we need to admit that there isn't real FF feeling plus the story way too plagiar. I absolutely didn't feel like replaying it immediately after the first playing.
FFIX:
Square tried to put FF1-5 into 3D. They didn't succeed. I liked the game (much better as I did FFVIII) but it was too easy and the final boss was so easy that my sister killed it with ease... My only big complaint is Zidane...
FFX:
No! Too much emphasis on machines! The magic went out from the FF series! This game didn't feel like an FF game (like the VIII didn't, either). Plus I hated those religionfanatic yevonites, as well as the rude Al Bhed.
FFXII:
I haven't played it, but... MAN! It's enough to watch only the intro to see that it's a so big Star Wars ripoff that it's wonder that Square haven't got sued! Even the beings are the same! And what about the main characters? It's a joke! That girl looks like Yuna (FFX) and the main character is not only gay, but looks like Tidus (FFX) and Zidane (FFIX) together! Plus there is that man who is a Laguna (FFVIII) ripoff.
Only the 6 and 7 are worthy.