I have been to Copper top. I would rate it very good but #1 in the USA? Not sure about that.
Big Pine is a tiny little town on highway 395 on the way to Bishop & Mammoth Lakes. I pass the place once a month because I live in L.A. and have a place in Mammoth.
The chef is out there almost all day grilling Tri-tips Santa Maria style on a big stick burner. On a nice day the line is 40+ people deep
Part of the draw is that it's definitely the best place to eat on the 300 -mile trip from L.A. to Mammoth. I may stop there next weekend!
As far as good BBQ joints go, Bludso's in Compton has the best brisket I've ever had. It's a religious experience.
The con's are that you have to go to Compton and even if you call in your order you are looking at a half-hour wait on the sidewalk in the ghetto, and they have no seating-strictly take-out.
Also, I've heard that their quality has been slipping as of late.
They have opened an actual restaurant on the west side, but I have yet to try it. Also, they serve it at the Forum (concert venue), but I highly doubt it's as good.