I haven't read this thread much yet, well not at all yet because I just joined this site, but I'll throw in some opinions...
I'm American but I personally think British music kicks the dog **** out of American music for the most - especially in the realm of rock and roll.
Any country that produces the likes of The Beatles, Led Zeppelin, The Kinks, The Rolling Stones, Oasis, Cream, and even "discovered" Jimi Hendrix should hold the all-time crown for best rock music, even if they didn't invent it.
To be frank The Beatles, Led Zeppelin, and Oasis as a 3-group unit, I believe is better than any 3-band unit of American bands in any configuration.
Now with that being said, I agree with the above poster who mentions that America has invented most of the best styles of popular and/or well known globally successful artforms.
To be even more specific, African-Americans (I am one as well) are really responsible for the vast majority of influential/successful styles (rock, blues, jazz, r&b, etc. etc.) so if we want to have a fair discussion - shouldn't this be African-Americans vs. Brits? That's a music better fight since for every Lennon there is a Michael Jackson and for every Bowie there is a Stevie Wonder
For every Morissey there is a Prince, and for every Elvis there is a Chuck Berry...
The list could go on, hehehe, but you get my point!
The Brits win for rock history, Northern Soul, and most of the modern good ****,
But it all start in America, specifically Black America, so hehehe who knows? Good debate though