I've owned & still own a lot of brands so I'll post my experiences, regardless if the OP got carried away by squirrels or if he's still on the board:
First was a Rock River Arms 16" AR, well made, heavy profile unlined barrel, VERY accurate, WAAAY overgassed. Great quality but not cheap.
Bravo Company/BCM is my best AR, and the most expensive by far. I mainly bought it cause at the time there were few options for a pencil profile lightweight midlength upper. Good chrome lined barrel. My favorite.
At least a half dozen PSA uppers on a mix of PSA, Rock River and Anderson lowers. I don't think I paid over $300 for any complete (with bcg) upper. Most are various calibers like 7.62x39, 6.5 Grendel, 9mm, etc. PSA is always a safe bet, good value for the money and good customer service.
Had one Anderson 10" 5.56 upper that was as accurate as my BCM but let it go cause while I have a few AR pistols in other calibers 5.56 was too much blast.
I still have a Radical Firearms 10" 7.62x39 upper minus bcg. Shoots fine, nothing loosened up. Bought it cause it was SUPER cheap on sale from AIM Surplus and I already had a good bcg. But RF's customer service must be lousy from what I've read so I bought it knowing if there were issues, it's on me.
Bought two Alpha Shooting Sports uppers in 7.62x39 and 5.45x39, both good shooters. No complaints.
Bear Creek Arsenal 6.5 Grendel 20" stainless upper- on sale crazy cheap a few years ago with a bcg, VERY accurate shooter, has held up well over the years. I'd recommend BCA if you're on a budget. Their customer service seems to be good and their selection is close to PSA.
I've swapped just about every upper here listed with every lower including Plum Crazy, New Frontier, and Mag Tactical. Everything fit everything with no excessive slop or functional issues.
And don't buy a polymer lower....ask me how I know....