For hunting ARs, avoid fixed sights integral with the gas block. The front post sight, especially, can interfere with your view through the optics. If you really want iron sights, folding back-up sights are the way to go—but to truly get the most from your rifle, you need an optic. Select your scope just like you would for any other rifle, but consider using quick-detach mounts to mount to the gun. That way you can quickly swap out multiple optics without (theoretically) losing zero. The combination of a traditional scope with a mini reflex sight, as shown, can be a good idea too.