After seeing the immense amount of extras found in the Saturn version you'd think that it would be a lock for the Definitive Version, especially considering that, to this day, it still has content exclusive to the platform. However, the negatives outweigh the positives and the title of Definitive Version belongs to another release.
Now I known the PS1 purist are already upset with me after seeing the PS4 logo, but please just calm down for a second and let your objectivity decide.
The PS4 is a great upgrade to the PSP version that allows you to play Symphony of the Night on a much larger screen with minimal lag, and nearly zero slow-down. On top of that you get more items, a new boss, and a quick save feature which is a must for modern gaming. Oh, and by the way, did I forget to mention that the original game director oversaw the development of this version of the game [PSP technically]?
If you've never played Symphony of the Night before Castlevania Requiem is the Definitive Version, however, if you're looking for a new experience Saturn might be the way to go, and yes, the original PlayStation version is still a great option.