I was asking the same question about the gas system vs. piston about 8 months ago and received the same replies you are getting. I decided to start building my DI rifle when the prices of the Colt 6920's bottomed out. I ended up picking one of them up a couple months ago. The reason I decided to go with the Colt, besides the advice of the Koolaide drinkers out there, was that the Colt 6920 was built in almost exactly the same specifications that the military's M4 was and the resale on a Colt will always be higher than most anything else out there (that's not to say that others don't build an equivilant or better rifle, but everyone know's who Colt is. How many outside of the AR enthusiasts know of BCM, LMT or Daniel Defense?)
The question for you is, what are you buying a rifle for? If you don't plan on joining the Michigan Militia or expect the end of the world next year, you may find that Rock River, CMMG or S&W, to name a few, build incredible rifles for the money.
I would consider the following when buying a new AR:
- Chrome barrel for longevity or Chrome Molly for accuracy (some folks like Chrome just like Uncle Sam does)
- 1 in 7 twist to allow the use of heavier bullets or 1 in 9 for 62 grains or less (which is most of what is sold out there)
- Do you want to pimp out your gun with lights, lasers and red dot sights (if so, try to find a rail in place of the handguard. If you want a red dot sight, then you will want a flat top receiver)
- What length barrel? (if you want a shorter barrel, then the gun will be put under more stress and you may need a beefier bolt carrier group and m4 feed ramps)
Like I said, what you want to use the gun for will determine what you want to buy and how much you may need to spend to get a durable rifle.
Jeff