If you are talking about shooting long distance, you need a lot of adjustment range. That eliminates the Monarch right there (only 30MOA adjustment range).
As far as the other choices go, a lot comes down to how much you are willing to spend and how much adjustment range you need (i.e. how far you plan to shoot).
With Elite 6500, 4.5-30x scopes have about 50MOA total adjustment. 2.5-16x42 scope has about 70+MOA of adjustment, and I generally prefer this model.
With Sightron, in order to compete with Elite 4200 and 6500 scopes in terms of both price and performance, you should be looking at S2 Big Sky and S3 scopes. Regular S2 is pretty decent (similar to previous generation Monarch in performance), and good for the money, but competes in a slightly different market segment.
S2 Big Sky 6.5-20x50 and 6-24x42 scopes have 60MOA of adjustment.
S3 6-24x50 has 100MOA of adjustment.
A few other considerations: if you plan to use high magnification, you should really be looking at scopes with fairly large objective lenses. 50mm provides a visible edge over 42mm once magnifications get a little higher.
All that set aside, I would suggest you first figure out how much you want to spend. Assuming you want top end magnification of 20x or more, here are my suggestion in different price ranges:
~$500: Vortex Viper 6.5-20x50 with MilDot (30mm tube)
~$600: Sightron S2 Big Sky 6.5-20x50 with MilDot (1" tube)
~$750: Sightron S3 6-24x50 with MilDot (30mm tube) or Bushnell Elite 6500 2.5-16x50 with MilDot (30mm tube) if you are willing to put up with lower magnification.
Honorable mention: Hawke Frontier SF 4-16x42 scope is a very well laid out and reasonably compact scope with ~80MOA of adjustment range. Hawke Frontier SF 6-24x50 has ~50MOA adjustment range.
I reviewed the 4-16x42 version a while back and thought it was a very nice scope. If you decide to try the Hawke, ceylonc is selling a couple of his scopes in the for sale section at very attractive prices (~$400).