I like to build (and shoot) the AR platform. I have a few, including 2 SBR's (a SIG that I won in 5.56 NATO, and one I built in 9mm and it is suppressed) I've built them with standard lowers and side charging lowers, one with a slick side lower, and a AR pistol in 9mm. I also own a Ruger SR556 and a AR556. The very first AR I ever bought (in 2006) is an Armalite AR-15 (20" heavy barrel, fixed carry handle, A2 buttstock (fixed, not collapsible). It goes well with my collection of the US's main battle rifles (alas, mine are all semi auto versions, I don't have the moola for select or full auto versions)
I like the AR platform, I shot in competitions in the USAF (and medaled) with M-16's and I just like them.