I do love IX but i have to say VIII is the best IX would probably be second to it though, i didnt really enjoy VII as much as i would have without all the hype that comes with it.

I think VIII is best because....
The protagonist is far better in my opinion as is the Gunblade.
The card game was soo much better.
The in-game music was better (i think that's kind of a weak argument though haha)
The FMV sequences were better in my opinion ( only because they are called humans in IX and they don't look like Humans at all)
I have yet to find a fist type that is all free spirited and aggressive (im some way into disk 2)
There was a tutorial on Summons ( i was just wondering why i couldnt summon Ramuh, Stupid Peridot)
Freya,Zidane and Garnet seem like the only mature characters in the whole game so far( It felt a lot like babysitting)
Quina annoys the crap out of me.

Although IX does have it's Good Points:
Garnet is so much more tolerable than Rinoa.
Ultimecia was physically known about in the game for an amazingly short amount of time.
Moogles are fun save points
The in-game graphics show more detail.