I have built quite a few ARs, and as long as you stay away from the overseas made parts, you will more than likely be satisfied with the results. I have used Mega, DPMS, Anderson, and aero precision lowers, and honestly could not say anything bad about any of them, as they all seem to have the same fit to any and every upper I have. If you are going to build something milspec, go with a 5.56 chamber and a chrome lined FN barrel if possible. Otherwise just go with what you like for function or looks, as these tend to become a custom build to suit the builder. Most of my builds are 5.56, with the exception of a Wylde chamber on a 18” bull barrel, and a 204 ruger stainless fluted barrel build. I try to stay with a 1:7 twist if possible, as I want a rifle to stabilize a heavy bullet. Speed doesn’t equal accuracy... If I ever do another, it will prob be in 17 Remington, just for something different.