I've used both side by side, both are pretty good glass for the price. The Leupy has slightly better glass, and is a bit more user friendly, but was a bit more spendy. The Leupy is US made (which sold it for me) and very tough for a lower end scope. Mine's been beating around my pickup for 3 or 4 years on my RRA, dropped in the snow, had 2 kids stand on it in the backseat a zillion times, truck door has slammed the butt of the rifle hard enough to knock it into the other door (was in a soft case, but still a bad move on my part) Still passes the box test.
The Nikon M223 is a lot closer to the Mark AR. Even the price is closer.