Pat espouses Colt parts -- and original factory Colt parts only. I don't personally own an AR -- though one of my significant others does.
I am a Colt lover, yes. But there are other good quality parts available. If interested I happen to have a few parts "laying" around:
Stripped lower receiver (R Guns)
Assembled upper receiver (Smith & Wesson) + 14.5" barrel (Colt) + pinned flash hider (Bravo extended A2) + delta ring (Colt)
bolt carrier group (Bushmaster)
And some other misc. parts.