I think I mentioned this under the shotgun forum, but I think by far, the highest quality producer of AR's out there is Wilson Combat. They make a variety of pieces to suite most needs, and use nothing but the highest quality components, often custom crafting pieces to ensure the best possible fit and finish.
Stag gives you the best quality for the best price IMO. After that Bushmaster comes second in quality and price. I love my Colt, but limited availability of their L.E only line combined with high price turns alot of people off.