My opinion on most of them has changed in various ways and degrees but at the top of the list would be FFX.

Loved it when I first played it, but in the years that have passed since then, my appreciation for just about every aspect of the game has gone down, some more significantly than others.

On the flipside, an FF I appreciate more now than I did when I first played it is FFXII. I didn't dislike it, but I definitely like it more now. Partially because I initially played it in Japanese before I really knew any Japanese (didn't want to wait a year for the EU release), but also partially because of various aspects of the game's design that I can simply appreciate more these days.