I own or have owned all three brands you mention. All reliable. Price wise, Colt is more expensive, with Bushmaster and DPMS close to each other. Stag and Rock River are other popular brands with a good reputation for quality. Or, you can buy a stripped lower receiver for about $100, then order a kit, which comes with every thing except the stripped lower, for $465-$475 or so, plus shipping. You assemble the lower parts in the lower, add the stock, and snap the assembled upper half to the lower, add a sling of your choosing and a few magazines likewise, and you have it, at an even better price than any comparable model of the above. Check out AR15 dot com for more opinions than there are you-know-whats on which AR is most reliable. I believe it mostly comes down to which roll mark you prefer on the lower.