I do not have a Nikon Monarch to compare against but I really like my Vari-x Leupold 6x18, with the LRV reticle. I often use the standard turret to dial moa if I need to shoot past 550 yards. I use it on a 25-06 and shoot coyotes in the moonlight all the time. I like it so much that I bought a vz3 6.5x20 30 mm tube 40mm objective with the Varmit reticle hot rod wha-zoo scope for a long range saddle gun that I put together........I like my 6x18 better in low light, I like the 6x18 better period! I also think I like my 2 vari-x 4x12ao's better then a Vari-xIII 4.5x14ao that I have sitting on a shelf.
I have never tried a Night Force scope but I have sold a zeiss and Swarovski scope that I recieved as gifts because, I just did not like them.
I think, I may either have a Leupold fetish, or it might be the fact that the Leupolds have just never failed me, so it might just be full on love!