Nightmare has the sole advantage, simply because of Soul Edge period.
Regular Jin was taken down by a group of Mishima Zaibatsu Soldiers, while an entire army was completely wiped out from existence by Nightmare. Devil Jin would actually pose a good challenge to Nightmare, however again, Devil Jin is completely out of control, not being capable of controlling his abilities, in which he would go wild and wreck less, as seen time and time again when Jin goes in DJ mode.
Nightmare can also channel out powerful energy shockwaves from Soul Edge...like the one that took out the army, and is also represented within the SC game as well (obviously smaller so that it isn't broken).
If Jin was actually fighting someone that wasn't either Sophitia, Mitsurugi, Siegfried, Xianghua then I say he would actually have a good chance of winning. The reasons why I named those characters is because Sophitia is being given weapons from the Gods as well as having their blessings and has destroyed one Soul Edge before back in Soul Blade, Mitsurugi is one of the few characters who does not have some "super entity/weapon" help that would be capable of contending with Nightmare toe to toe, Siegfried wields Soul Calibur, and Xianghua also wields Soul Calibur as well, which is the exact opposite half of Soul Edge, putting them on the same lvl as Nightmare.
I really like Jin Kazama alot...but this match up is in Nightmare's favor 🙁