I have one of each. The Mil-Dot is in a 3.3-10x44 AO Monarch. I love it and use it for everything from foxes up to deer. Just remember the Nikon Mil-dot is in the second focal plane, so the measurements only line up right on one power setting. In mine it subtends 3.6" at 100 yards on 10x only. My understanding,(as advised by a rep at Midway, FWIW), that the higher mag scopes are set to work on 12x. If you get the Mil-dot, I highly recommend getting a Mil-dot Master and learning how to use it.
The Nikoplex is pretty standard, but I like it better than Leupy's duplex and WAY better than their fine duplex. Mine is in a 6-24x50SF Monarch.
I feel both reticles naturally draw your eye to center quite quickly and effectively. The Mil-dot has the advantage of acting as a back up rangefinder.
If you can, look through both and see what you like best.
Let me know if you have any other questions I might be able to answer.