Aero receivers are decent. I have a rifle that was pieced together from a stripped upper and lower from Aero and it’s got a good fit/finish. Also have used Aero BCGs without issue. I just finished putting one together with a Wilson Combat barrel but haven’t shot it yet to comment on accuracy. The barrel itself seems to be well turned, fluting is nicely done. My go to barrel though is White Oak Armament. Each one I have from them is highly accurate, and they have a friendly knowledgeable staff. Good triggers and barrels are where it is at for accuracy. The third most important thing is probably fitment of the barrel to the upper, and upper to lower slop. Triggers, I’ve got Timney, Velocity, and TriggerTech right now. Have used Geissele before also, just a preference thing really, but get a good one.
They’re fun to put together regardless.