Simon vs. Urzaia
The Nye essence gives Simon the edge here, but only at first. Honestly, based on the way Simon fights, he wouldn't start out a duel against an unknown opponent with an all-out offensive blitz. And that would be his best chance.
Urzaia can take a hit from Mithra. His weapons can stand up to it, and his Soulbound Vessel can stop it as well. On top of that, he has the strength to (more or less) match Simon and enough reaction speed that he wouldn't be completely overwhelmed by Nye essence unless Simon pushed it to the limit from the very beginning. Plus, he's dueled a hundred times more people than Simon has.
Given that Simon starts the fight trying to be conservative with his powers and then ramps up, Urzaia wins. If Simon knows how much of a threat he is and treats him that way from the very beginning, Simon MIGHT take it.