I recently decided to get a Red Dot for my AR-15 build out, I opted to go with the Vortex Sparc Red Dot. I mostly decided to go with it after the review by Mac on the Military Arms Chanel. He does a good review and some durability tests. Check it out.
Some things to note, I’ve found that with red dots and holographic sights, the way my eye is, causes the dot to be a little misshapen and not clear. This is my eye, and not the optic. In the video below I discuss some of the details around that and show some pictures and video of the reticle. Check it out!
You can pick one of these optics up on Amazon for $199, http://l.santsys.com/14MwsXs