On the whole Americans are surpassing the Brits pretty thoroughly at the moment. Louis CK, Bill Burr, Doug Stanhope etc are all killing it compared to UK stand ups. There is some decent stuff going on but shit tv panel shows are definitely killing the scene over here. Jim Jefferies is pretty good as well and an Aussie working mainly in America.
Obviously classic stuff like Bill Hicks, Bill Cosby, Richard Pryor, Jerry Seinfeld, George Carlin, Billy Connolly etc from the old days is all worth watching.
There's a few more niche uk comedians like Ross Noble and Jack Dee that I like watching but I'm unsure how well either of them would transfer for Americans.