The USA made Rock -N-Roll...Jazz....R&B...Hip Hop....Country.
You say that like they should be proud of R&B, Rap and especially country. Old school R&B is tight, but since about 1990 its been the 2nd worst type of music around, country has that **** on lockdown though.
Its probably fairly even though, England absolutely pumps the US when it comes to electronic music and rock and roll which are probably the 2 biggest forms of music overall. Throw in punk(you create it you get credit whether its good or bad) and its very arguable.
I'd go with England, because in the forms of music I listen to they have been better. Even their Hip Hop has been at least as good for the last 5 years and they dont have country dragging them down big time.