Noveske makes good shit and I've used a lot of their parts over the years. The MUR1 is another really good upper I use. One thing I noticed about "milspec" cheap uppers is that some tend to vary --when I switched to KAC lowers, I noticed some cheaper uppers would leave large gaps in the rear. They'd pin on, but they didn't fit well. The Noveske, MUR1, LMT and I wanna say a BCM upper all fit. I have a Colt upper out there I think will work well too. Oh, an AAC upper will fit too, whatever they used.
A good 7075 forged upper made by a quality company is usually good to go. Part of what you're paying for besides tolerance of the part is the finish they use too. There's a big difference there.
But best bang for buck IMO is the MUR1, wanna say they're 7075. It's a solid part that usually fits well. Noveske used to use those a lot until they started making their own version and they tend to fit Noveske lowers very well FWIW. I don't know if it helps having a beefier upper like that, it does make me feel better about the Grendels I guess, but it's a good upper overall regardless and I don't think it's that much heavier over a typical forged upper.
As far as accuracy goes, I've taken to facing the upper with a lapping tool, it's easy enough to do. I've noticed most of the quality uppers are already pretty flat. Then Loctite 620 to bed the barrel to the upper. It's a permanent installation, meaning a barrel change includes a new upper receiver, but it makes it makes the whole thing solid.
Not an upper, but the KAC URX4 handguard is a one piece unit that can torque on higher than regular barrel nuts. Being one piece and tight like that, it basically makes a bedded upper into a monolithic piece for all practical purposes. I haven't found anything better.
