The Euro Diamond and Signature Select use the same glass and coatings, the only difference is 30mm tube vs. 1". Their are also different power ranges and reticle selections. The same can be said for the difference between the Nikon Gold and Monarch.
These scope are hard to compare because they are both very good. The Nikon is a little bit brighter but the Burris is a little bit sharper. The Nikons are easier to use because they have a more forgiving eye relief (Burris' is some what critical). Although both are rugged durable scopes and not prone to malfunction the Burris is quite a bit more robust for several reasons. They are built like tanks, everything is done to the extent of over kill.
Here is a graphic showing some of the construction features of a Burris compared to the competition.
