I can't really say what the best PS1 game is for me for certain. RE2 was for sure great, but back when I played my PS1, I was about 7 and I never actually managed to beat the game myself, but I watched my dad play through most of it. I did manage to beat RE3 though and in my nostalgic mind, I like RE3 more.
I also played these games quite a bit and I consider them my favorites, although some may not actually be objectively "good" games. My apologies for my memory is vague and I don't own my PS1 or any of the PS1 games anymore.
-Syphon Filter Series (1, 2, 3)
-Crash Bandicoot Series (1?, 2, 3)
-Spyro the Purple Dragon Series (?1, 2, 3)
-RE2 and RE3
-Bitmap Brothers Z
-Red Alert (1 & 2?)
-Dyno Crisis (1 & 2, from what I recall, 2 was horrible)
-Nuclear Strike
-Nuclear Dawn
-Silent Hill
-Alone in the Dark
-Army Men Series (love those games, don't remember all of the games I had, but I think I had Sarges Heroes, and Air Attack 1 & 2)
-Dune
and tons more I'm sure, just don't remember all of them.