I have had great success with the Sightmark QD Ultra Reflex Sight. Can be found on Amazon.ca with free shipping for about $120.
Its rated by the manufacturer to .50 and was designed for use on the AR-15 platform. Holds a solid zero, super crisp reticles (4 different reticles you can use) and is in between an EOTech and T-1 in size.
It creates a very unique look:
It also co-witnesses perfectly with Daniel Defense BUIS as well as many others including standard AR iron sights:
