Every final fantasy game is different in terms of gameplay, story and characters, themes, music. If you like the genre, I think it’s worth playing the newer games and rediscovering the older ones. Every entry is unique, and they tend to resonate differently with different people, so it’s hard to point at one and say “play that one, it’s the best”, but IX is usually ranked pretty high among the fanbase. I don’t think it’s the best JRPG ever (that would be Xenogears), but I rank it pretty highly, too.

I also never played it, but X-2 is (as far as I know) considered pretty mid or even bad by some, so if you’ve been put off by that one, it could be worth playing at least its predecessor.