HK is ridiculously overpriced and apparently hates civilians as they won't sell anything but pistols to them. I'll never buy anything from them, unless I'm getting it from a private owner and HK isn't getting any profits from the purchase.
If I were in the market for a gas-piston AR, I'd want a Patriot Ordnance Factory or LWRC rife. Made in the USA, and the POF has a silicon nickel plated operating system that is said to make cleaning much faster and easier.
Really though I'm more a fan of bullpups when it comes to 5.56x45mm; I wouldn't want a 5.56mm firearm if the barrel wasn't at least 18.5", preferably 20, and a barrel that long on a rifle of conventional layout would make it cumbersome in tight spaces.