I have owned (complete rifles) Bush Master, Colt, and Oly. Having said that, I would rule out the Oly because of tight chamber/non chrome Bbls. I would rule out the Colt if it had the big pivot screw lower instead of a mil spec push pin lower like all other ARs. I like the idea of interchangeable uppers. Like others said, I hate the large pin fire control parts on the consumer Colt. I bought some RRA lowers, and uppers last month. They were priced cheap, to my surprise, the quality (fit and finish) was just as good as my Bush Master. Reading topics here on RRA products have revealed the same findings. Everybody praises their NM trigger. If I was buying a new upper, the Barrel would have to be chrome lined and fluted. You can shave some weight off the front end. It seems back in the mid eighties after the A2 was adopted, everybody was pushing the heavy barrel because they would not bend and less barrel whip-it was better than the pencil barrel. Now the military has cut some weight off with the M4 design. I like the idea of the fluted bbl-lighter, more surface area for cooling, and a more rigid bbl to boot. Just some ideas to think about.