Well, USASOC and JSOC used Daniel Defense uppers for around a decade and Colt has been the staple for the U.S. military in regards to the M4/M16 platform for over 50 years, so those might be your "Operator Tier" rifles. The Aussies and New Zealand went with LMT for their M4 equivalent and the Army of Denmark went with Colt/Diemaco for their rifle. That should sum up what the rifles of choice are, especially on a global perspective. Many people here have built their own rifles using parts from all of the companies listed above. Brands like Noveske, Hodge, KAC, and some of the other boutique brands do make some decent stuff, but how much of it has been proven beyond YouTube videos and Instagram, minus KAC since they hold numerous government contracts. Geissele just recently broke into the MIL contract game and people are still bitching about their products not being up to standard, even though they do make some decent stuff. I've been fortunate to have had no issues with my Geissele MK8 and MK4 handguards. Sig seems to have found a niche in the military realm with their 300 B.O. LVAW thing, as I saw several of General Miller's PSD guys carrying them while I was in Kabul in 2019, and when I got to vacation there again in August of 2021. The 75th and the SF guys that I ran into in '21 were still rocking Colt M4A1 lowers with Daniel Defense M4A1 or Mk18 uppers, and even the Department of State dildos were rocking the Mk18 in an all black anodize configuration. I did not see one Hodge, Noveske, or Radian rifle either of the times I was in Kabul, or in any of the other cities or provinces in my other previous travels to Afghanistan. But, to each his own, and that's one of the greatest things about living in America. Buy what you want and use it to the best of your ability.