PS1 by a mile. Every other version has either worse graphics, removed cutscenes and/or fucks up the music score (including the GoG version, unfortunately). The soundtrack plays a BIG part in making the first Rayman so good, so playing a port with a worse soundtrack is not worth it, imo.
Even better, Rayman Redemption is a free fangame that contains all the content from the best Rayman, and expands upon it. I'd say it's the best way to experience this classic.
EDIT: Although I wholeheartedly recommend Rayman Redemption, it would be a bit irresponsible from me not to mention that it is a fundamentally different game compared to the original: a non-exhaustive list of changes:
- All power-ups are unlocked from the start (which makes for a less slogg-y beginning, but does make the first few levels a tad bit easier)
- Most levels have been expanded, either with longer screens or entirely new levels, boss battles and collectibles.
- An overall less grindy experience (more lives, being able to unlock additional hit points and gloves power-ups).
- Different physics (such as: being able to hit small enemies more easily; helicopter-hair being more similar to how they work in the sequel games; Rayman now stays in place when he is hit instead of jumping backwards, which makes the eggplant-riding challenges a LOT easier).
- Some QoL features, such as keyboard/controller setup, options for resolution and aspect ratio, gloves power ups being visible on Rayman's sprite, full-charged glove having a different loop animation from the normal throw animation, etc...
TL;DR: If you want to experience the original game as it was intended, PS1 is the best port to experience it. If you want a more modernized experience, Redemption is the way to go.
Quick review: while having the choice to play the Rayman 1 port you like the most is cool, there is not much reason to play anything other than the PS1 port except for the novelty of it.
Even then, the sountrack has been altered: this new one was made by the same person who did the Origins/Legends soundtrack. While I love the soundtrack of those games, Remi Gazel's original soundtrack for Rayman 1 is iconic and it's a bit insulting to both the fans that grew up with it, as well as to Gazel himself who sadly passed away a few years ago, not to be able to toggle the original version. Compare Bongo Hills' original soundtrack with the new one, it's a completely different experience - why can I toggle between five different ports, but I'm unable to experience those games the way they were originally intended?
The hyped SNES prototype is the same rom that was dumped on the internet a decade ago. Nothing new to see here.
The artbook and dev commentary is cool, although the value for those things is subjective.
Overall, I'd say it's not worth the price of admission unless you really, really want to take a look at the bonus material bundled with the games. Either play the original PS1 game on Duckstation, or the fanmade remake Rayman Redemption.