I would go MOS. I got my first slide milled for a Burris FF3 and now I'm stuck with that dot forever. I do think that the milling is much better for reliability of the optic staying on. But, It now sits in the safe and I use it as a backup gun. If you were going to go with something like an RMR i think the milling would be good as those will probably have the same footprint for the foreseeable future. I use the forward controls plate with the DPP. I have had it come loose a couple times on the MOS.