As mentioned, consider first what your intended use is, then build around that. The .223 is a compromise; it gives you magazine capacity and flat trajectory, it costs some terminal energy. The benefit of the .223 and the AR platform is that it creates a very lightweight package with plenty of stopping power for man-sized targets on down to varmints. Yes, a .308 is going to be a better man-stopper than the .223, but it kicks more and the gun weighs more. If you’re going to go the route of an AR in .223, keep ‘lightweight’ in mind, and build to that ideal. If you’re going to commando your AR with lights and all sorts of other add-ons, you’ll cross a line where the gun is as heavy as a .308 with all the drawbacks of the .223. Are you going to get an aluminum 4-railed fore-grip? Well, aluminum weighs a little more than the plastic, and encourages you to add things to the rails. Just try to keep the ideal picture that you formed when you buy or build.

Personally, I don’t like the 16” barrel with the carbine length gas system. The carbine length system is really for 14” barrels, which we cannot really own (yes, there are exceptions and ways around that rule). I prefer the mid-length gas system for reliability, more hand space, and looks. It also allows you to add a bayonet for when you want to take a picture of the gun. ;)

I also prefer a 1:7 twist barrel, it allows you to shoot heavier bullets.

Whatever you decide to do, research first, then buy or build. Decide a purpose and remember that purpose when you accessorize. Don’t fall into the trap of attaching a load of gear to the rails just because you want it to look cool.