This is where looking through these scopes makes a big difference. In general, I have been very pleased with the Nikon Monarchs and new gen Buckmasters I have used. They have awesome glass at very reasonable pricing.
My eyes just don't like the Luppies enough to justify the premium they ask for. Many, many shooters don't feel this way.
My only experience with the Burris Black Diamond is through a Pentax lightseeker 30. The same or different, I cannot say. However, the Pentax has decent optics and the ability to see mirage 'clearly' and still resolve the image. Kind of bizarre. Only scope I have ever seen do this.
Turrents are ultra stupid at 7.5min per revolution. For that one reason alone, I would not recommend anyone share the grief. I am sure that this wonderful feature has since been removed.
The Luppy and Burris are much more money then the Nikon. The Nikon is every bit as good optically (I feel better actually) and mechanically reliable. You will be very happy with these optics if you go this route.
Now if really on a budget, I will recommend again, the new gen Nikon Buckmaster 4X14 side focus. Very nice optics for dirt cheap.
I also am very fond on the Elite 4200 series of scopes and feel their optics are second to none. Mechanically superb. A 4X16-40 will do everything you want for even less money then the Monarch. If you want a bit more mag, the 6X24 is a great buy.
Jerry