Oh man, you can't expect me to make this choice!

As far as FF's go, these 2 games are by far the most accessible in the series. IX has the entire manual in-game with the select button while X blatantly shows you the mechanics of Final Fantasy early on (certain characters for certain foes).

As far as stories go IX felt like the same Fantasy world i've already been to a million times, whereas the world of X was something new. However IX did it very well, and it tied together all the games really nice in basically summing up everything that the series stood for in 4 discs.

I remember beating IX and then the same time next year getting PS2 and FFX and playing till I beat that. I'm not quite sure which one is better, but they're 2 of my favorite RPG's of all time.