IIRC it was originally built for Saturn and there were a number of graphical downgrades in the conversion to PS1 along with reduced sound quality. Loss of shadows on 3d buildings, loss of various 2d effects, issues with textures, less stable frame-rate, maybe more that super fans have documented online. It also came with a couple minor upgrades e.g. better video bitrate. Nothing is different enough to affect playing the game. The completion of the English patch is relatively recent so that probably explains the renewed interest in the Saturn version.

The HD version spruces up the PS1 version but didn't go as far as restoring everything lost from the Saturn one.

So none are really definitive but the Saturn version is usually said to be the best. The PS1 has the advantage of greater availability and can be emulated on a potato. And the HD one is on sale for modern consoles.