Don't taint your first SOTN experience by playing the Saturn version. PS1 version is far superior and actually cheaper. SOTN is a goddamn masterpiece, easily in my top 3 games of all time.
I'm not quite sure though. Saturn version has some extra areas, better music, more items and two extra characters available from the start. I understand the graphics are a little worse, but is it a big deal? Or is there more that I am missing.
Saturn version has better gameplay.
Graphics aren't fully intact, but if the Saturn version looks bad, then the Playstation version always did as well.

it's general knowledge that the saturn was a cheap take over from the original playstation version with a lots of downgrades involved.
it's has no transparencies at all -> makes many thing look far worse (mist, waterfall, aura stuff etc.)
looots of annyoing slowdwons, where there shouldn't be any -> better gameplay where?
more often and longer loading times
sometimes using different resolutions which make look things strange and blurry
entirely missing back grounds
less animations of certain enemies
downsampled fx
totally crappy done running horse at the beginning (don't even know of why they changed that completely from the PS version?)
the only good thing the saturn has are few added stages, which were all unfinished take out from the PS, which KCEN decided to add. while they're nice to have them (especially the cave one one for its music), they look unfinished and don't live up to the rest of the game.
also that you can choose different characters from the beginning, doesn't really make anything better. you're just spoiled for choice.
it's kind of a similar situation like with the PCE WoT -> MegaCD LoT port.