I built myself an AR with an Aero Precision lower, upper, barrel, bolt carrier group, barrel nut, and hand guards. I've never shot it from a bench rest, but I'm pretty sure I'm the limiting factor in the system when it comes to accuracy. Parts fit together very well with little to no "play," and I haven't had a malfunction with it yet (but only ~100 rounds through it). Would a Bravo Company, Daniel Defense, Sig, or Noveske probably be more accurate? Sure. Would they cost a bunch more? Probably.
I'm happy with my AP stuff. If I build another AR (probably in .308), I'll probably stick with AP for the upper/lower... Might go elsewhere for BCG, barrel, trigger.