I have numerous Nikon Scopes, both the older versions and the new monarchs. The new monarch series are better, at least glass quality wise, over the Buck Masters.
Want to know a little secret? The older Nikons, which were great to begin with, had light transmission of about 88%, while the new monarchs are about 95%. It appears that the new Buckmasters are really nothing more than the older 88% Nikons with a new name. Other than that, the internal quality is, from what I understand, about the same.
I too cannot say enough about my Nikons. Granted, of course, that I believe that, for the same money as the Monarchs, you could get the Bushnell Elite 4200s which are, in my opinion, even a little better than the Monarchs. Of course you want the Buckmasters, and I can still tell you that they are good scopes for the money. Consider the Buckmasters to be the Elite 3200s of the Bushnell line.
Hope this helps.
Zachary