Nikon are good scopes, Leupold in the VX-III, VX-3 or above are great scopes, Ziess is a great scope that is better in some aspects than a Leupold.
If you are spending $500 on a scope DO NOT buy a Leupold. Get the Nikon, the VX-II line of scopes are not all that good in my eyes. I owned one and hated shooting with it. It was crystal clear and let in lots of light, but when I changed the power (6-18x40mm) the eye relief would change so much so that at 6x I was hanging off the back of the stock and at 18x I was riding the scope.
I traded that Leupold for a Nikon Monarch and I am in heaven. In your price range I would go with either a Bushnell elite 4200 or a Nikon Monarch Might even try looking at a Weaver grand slam or classic scope. These are all good scopes and provide a lot of options for your money.
Ziess is some of the best glass int he world. If you look at a lot of high end medical microscopes they don't come with anything other than ziess glass.
European glass offer more clarity and better light transmission than american or Japanese Glass. American glass is harder than European glass and resist scratches slightly better and can take a little more abuse. Japanese glass is up there but is not of the quality of American or European glass. It is however much less expensive than both other options.