Clear glass; easy to pickup targets - Athlon Optics Helos BTR Gen II 2-12x42mm 30mm Tube Rifle Scope, First Focal Plane

This is very fast moving optic with a moderate eye box allowing for generous positioning behind the optic when out in the field. After around 8x it does get a bit more restrictive, however the glass if clear enough to track a target out and around 800 yards still if you're stationary and on a bipod.

I would highly recommend checking out Brass Facts' YouTube review of this optic to get a better appreciation for this optic if you're looking to mount it to an AR. I think this is still a viable option if you're looking for a "general purpose" AR, but would also throw this into the mix if you want more of a DMR / SPR type rifle as well. Certainly not meant for PRS if you want to constantly be out at 200+ yards all the time, but this gives you the capability for easy target identification and tracking for a rifle that should be expected to occasionally get out that far.