I've traditionally built on Bushmaster uppers and lowers, always had good luck with fitment. They're not so easy to get ahold of these days though, it seems.
I have 7 uppers and 5 lowers on my bench right now. One Aero, two Spikes, and 3 bushmaster lowers, with one "Joebob's", one two Aeros, and 4 bushy uppers - all of these fit together very well. I have accu-wedges on hand for all of them, but none really seem to need them, other than making me feel better mentally.
Gotta keep in mind, most forgings are actually produced at one of about a dozen places, no matter whose name ultimately ends up stamped in the side. Plus, even within individual brands, they may not exclusively source from one forge. In this set of 7 uppers, two of the bushy's and one of the Aero's were Cerro forges, one bushy and one aero were Brass Aluminum forged, and I'm not sure what the JoeBob's upper was - kinda wanna say Martin Marietta.
Maybe I've been lucky.