You must be thinking of GTA II. GTA: Vice City was only on the PS2 (and later, PC).
Or GTA 1, which was PC game originally I think. However, as cool as those games were, I never considered GTA 1 or 2 to be the best of any system(PSOne included).
Is the game you are thinking of from the top-down perspective, or 3rd person and three dimensional?
GTA III was the first 3d GTA game and it was one of the big early PS2 games.
I & II were both PC games originally.