Way to difficult to say.
PS1 had all my dearest and nostalgic child hood memories, Crash bandicoot series, Tomb raider series, spyro series, syphon filter series, Gran Turismo 1-2, MGS1, Final Fantasy VII, the other Final Fantasy's, Chronocross, Vagrant Story, Tekken, Tekken 2 and Tekken 3 (my first ever game

), Resident Evil series and so on.
PS2 had the greatest library of AAA and AA games of all time, Devil May Cry, Shadow of the colossus, ico, MGS2, MGS3, GTA III, GTA: VC, GTA: SA, Dragon Quest series, Kingdom Hearts 1-2, Dark Cloud 1-2, God of War 1-2, Gran Turismo 3-4, Resident Evil 4, PES back when it was a AAA franchise, Jak & Daxter series, Ratchet & Clank series, Sly series and many,many more quality games
PS3 has MGS4; best game ever made ofc, and The Last of Us, second best game ever made and UC2 is also one of the all time greats so it definitely had quality, but I feel like PS1/PS2 had more quantity.
PS4 don't know yet.
Lol @ best games iyo.
But PS1 is combined into PS2 for the backward compatibility. PS2 has it HANDS DOWN.