Rather it was a game for a desert island or the last game I knew I'd ever play: I'd pick Final Fantasy Tactics for the PSX.
It was the first game I played as a teenager where I was actively daydreaming about it while I was supposed to be working at my first(ish?) job.
Like I literally couldn't wait to get home and continue building what I still consider the perfect team. Heck I bought a serial port PS1 memory card
reader just so I could move my saves over back in the mid 00s (which of course required a USB to serial adapter lol).
There's just something about that game and I don't know if it's the art or the gameplay loop or what, but I sure do love it.
No shade to the post about Tactics Advance above me (I like that game as well).