The LMT is actually coming from a reputable smith who does custom 1911's and AR's. He only sells LMT and Colt, because those are really the only AR's he has seen with consistently high QC standards.
My reasons for choosing the LMT over the 6920 are two-fold.
1: According the comparison done by Rob S. over on M4Carbine.net, the manufacturer who comes closest to milspec is LMT. The LMTs only have two things outside of milspec which the Colt has inside: straight roll pins instead of tapered ones, no parking under the fsb. The rest is all to Milspec...which means pretty much every gun that comes off LMT's line is made the same way, according to the same standards, and will (theoretically) run the same. Besides the legacy of the prancing pony, this standard has a LOT to do with m Colt commands the presence it does--in both 1911's and AR's.
I said all of that to get to this: the smith I'm buying this custom LMT from nib does a reliability package which includes replacing the straight roll pins with tapered ones, the only non-milspec part on LMT's outta his shop is that there is no parking under the front sight.
That said, the gun is 16" chrome-lined, 1/7 twist, flat top with troy folding stocks, M4 fore-grip, a Crane sliding stock, full auto BC, a2 flash hider, and some other things. Pretty much the LMT version of the 6920.
2: price. While the price I got on the Colt was good considering the hysteria, that 1599$ turns into 1715$ after taxes and paperwork. The LMT is 1450$ pls shipping and a 30$ transfer fee. No taxes. I get to save almost 200$ and get the same quality of gun WITH a reliability package perfomed by a well-respected Smith.