Nikon probably makes the best glass in the world. They make all their own glass, something other makers do not. Any other maker can buy Nikon glass, but it is expensive and they rarely do. Nikon makes more types of optical glass than any other manufacturer, that is one of their old boasts.
The usual argument is between buying one of those very bright Nikons or spending just a little bit more to get a Leupold which has undoubted build quaility and is American made. Whether Nikons will hold up on the heavier calibers is to my mind an open question. I just don't know and haven't seen any creditable discussion of this.
One of the features of the Buck Master series is a lesser quality of glass. Buck Masters have light transmissions of 95% thought each glass while the Monarch series has transmissions of an incredible 99%, per Nikon's specifications. This may seem like a small difference, but this adds up though each lens element very quickly. I did the math years ago and have forgot how to do it now. I don't know what other features are downgraded on the Buck Master series.