Go with Colt-preferably one with a serial # starting with LE. No not because its cool because it stands for "law enforcement" which it does. But because those particular models are assembled in the Colt Defense factory branch and put together with care unlike the mass produced "sporter" variety. The sporter models are pretty much the culls from the defense branch. I have a Colt M-4 6720. Its the light barreled version and it is quite the brass shucker. COLT ALL day, ALL weather, ALL battle conditions.