Mine was more a budget build than a top of the line tack driver. However, I happened upon a gunsmith who had acquired some barrel blanks very cheaply and he had them turned into custom heavy barrel and built into upper. Mine is a 16″ with a .223 Wylde chamber, which is supposed to be able to handle .223 as well as 5.56 NATO without missing a beat. I haven’t put any commercial .223 through it since I got lucky and bought a boat load of mil surp 5.56 when a gun dealer was going out of business a couple years ago. Doesn’t help you much since he no longer has any of those barrels. The upper receiver, free float handguard, and lower parts kits were all DPMS. The stripped lower was Superior Arms. I have not had any failures to feed or any other issues with the parts I used. The only thing I still want to upgrade is the trigger. The lower parts kit comes with a mil spec trigger, so I used that originally with the long term goal of replacing it.
In doing my research, there isn’t a lot of difference in components from most of the manufacturers – the low to mid price suppliers pretty much make everything to mil spec. If you want to get into the real high dollar stuff (highest quality available) from companies like Lewis Tool and Machine, you can dump several grand into an AR pretty easy.
I heard a lot of good things about Rock River Arms. If I hadn’t stumbled on my upper, I was going to buy one of theirs. They offer the .223 Wylde chamber in their .223 uppers and barrels.
Suzuki, one thought, if it was my AR, I would go with a flat top upper and a gas block with a rail on top. If you look back in the posts, there is a pic of mine with that setup. You can install open sights on the rails, and still have the ability to take them off and put on optics if you want to in the future.