I have a Colt LE6920 made by Colt Defense. Many Colts on the market, and I'm assuming those sold at Wal-Mart are made by Colt Manufacturing. Basically the same, but marketed different. The 6920 has M4 feed ramps, H buffer, MPI barrel, MPI Bolt, M16 BCG, Parkerized under the FSB, F stamped FSB, black extractor o-ring, and chrome-lined barrel and chamber. These are all mil-spec and enhance reliability. The only things that are not mil-spec are the FCG and the barrel length. With all that, my rifle will shoot right at MOA and can run dry and dirty without problems. It will keep running when others will begin to malfunction.
Now my personal opinion is if you are simply looking for a good shooter, then just about anything will do. I have a friend that built a varmint AR from a Model 1 parts kit. It shoots 1/2 MOA all day long and was much less expensive than my Colt. If you want something that is absolutely reliable, then make sure that it has the above listed features. (The H buffer is only for carbine gas systems)
Cuts, based on your criteria, the Midnight Dragon looks pretty good. If you're considering other options, I'd look at Windham for a good, lightweight, rifle length (gas system) varminter and plinker. They make one that isn't too heavy and all the ones I've looked at appear to be very well made. For carbines, check out CMMG or S&W. They make great rifles at good prices. If you want the most reliable and durable, then look at Colt (Defense), LMT, Daniel Defense, or Bravo Company.