Well, that depends....
Personally, If I was running an SBR....Say a Palmetto State Arms kit gun I'd put a Reflex on. I've always been sorta loyal to the Originator of the technology but have been known to subsidize our enemy and purchase lesser brands....Vortex put out a line of them recently and there isnt a loser in the pack!
On a 20 inch Barreled gun.....Like a Spikes Tactical I'd run one of the larger Vortex offerings as they are an excellent value for the dollar....The fact that they are an IN HOUSE item and happen to carry a lifetime warranty have BIG appeal too.
On a 16 inch barrel, like a Ruger AR556 I'd put a 2x Reflex like a Vortex or a Leupold.
Of course, An M1A would get nothing short of a Vortex or Nightforce SVH.Never go cheap on the optics!
And IF I had a Savage 110 FP It would get a Nightforce NXS and one piece mounts.....
Now, if one had a shotgun like a Mossberg 500, I'd run a flashlight and a 5 round carrier on the stock but keep it simple. Shotguns dont need no optics, you just point them down the Passageway and pull the trigger till you here some screaming!