A hard one to be sure!
Indeed the Wrath is more powerful physically and more adept in lightsaber combat but Darth Nox has far more knowledge of the force and it's secrets. I saw someone say that even though Nox defeated a dark council member it was because of the help of force ghosts. While technically true the force ghosts didn't help him/her (unless you went light side then they sort of did), Darth Nox basically enslaved them and used their power for him/herself. This is a classic case of brain over brawn, mind over matter. Those who aren't strong need to be smart and Darth Nox has the potential to be the smartest of them all. Example, look at the Emperor. We rarely see him using lightsaber combat at all but he has managed to survive for hundreds of years by manipulating the force to extend his life. Strength alone is rarely enough. I'm not saying that the Wrath is dumb, he obviously isn't but he far less adept in the force. In the end pitting them against each other is nearly impossible I think, the Wrath with his stamina and Nox with his force, it'll be an unending battle that probably destroys an entire planet. Now imagine those two teaming up, that would be an unstoppable powerhouse which would make their enemies sh*t enough bricks to rebuild the Jedi Temple!