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.

The game was built for the Saturn and ported to PS1 (versus being built independently for it). During that process, graphical fidelity and effects were lost and audio transcoded in a lossy manner. Sprites were lower quality, the water effects were worse, textures were downgraded, shadows were lost, etc.

This is a pretty bad demonstration since they took literally zero effort in syncing the two side-by-side til the end, but gives you an idea:

https://www.youtube.com/watch?v=UL6Z9xvt7h0

That being said, it's not so much worse that PS1 is unplayable. It's just that if you had the choice between the two, the Saturn version is slightly more pleasant to look at and listen to.

Shrug, if I blog about the joys of driving down route 66 in a '57 Chevy, I really dont have any obligation to give equal time to what its like in a '57 Packard. Its a Saturn fan site, so its just going to be Saturn-centric.