I really enjoyed both games, and they are in my top 5 of Final Fantasies alongside IX, VII, and Tactics Advanced 2. However, I did like X more, but only just.

For X, the sphere grid system and combat systems were things I absolutely adored. That's just because I love being able to plan my moves out, though, so seeing the order people would go in battle, or the path I could take for leveling, was a nice change up for me. Blitzball was a lot of fun, almost as good as Chocobo Hot and Cold, and anyone who knows me knows I've spent more time playing that than the actual IX game(Even though IX is still my favorite game OF ALL TIME). The story was really good, and all the characters except for Tidus (Yes, even Wakka and Jecht) were great, relateable in ways, and had very likable personalities. The only real drawbacks were the low number of locations and towns, Tidus, how too-easy the game was, Tidus, getting Lulu, Tidus, and Kimahri's sigils, Tidus, the only low-to-moderate replayability, and Tidus.

For X-2, I also enjoyed the leveling, class, and battle systems. It was new and fresh for the series, the full-active battle system(for the most part) was fun in a new way that X's wasn't, learning abilities was done awesomely, and the fact that levels only granted stat boosts rather than new skills meant you never had to grind, just plan your abilities well. New Game Plus was of course a really good thing to put in the game, combined with the higher replayability compared to X, and the divergent story arcs (even though they ultimately made almost no difference). The only drawbacks were that there still weren't many locations, there were almost no new places to explore, the 100% ending wasn't worth all the work for it, they screwed Blitzball up, and not being able to have any other characters in your party kind of sucked. Oh, and Tidus.