Its very hard to tell who's the better one, USA or UK. The UK wouldve dominated the 60s and 70s, bands like Beatles, Rolling Stones, The Who, Led Zepplin, Deep Purple, Pink Floyd, Eric Clapton, Queen etc.
But the USA have the best grunge bands in the late 80s, early 90s. I'd say the best are Nirvana, Pearl Jam, Soundgarden, Green Day, Stone Temple Pilots, all from America.
Its funny how you compare USA and UK, but when you've got the one of the best rock bands in the world, AC/DC, they wouldnt make the list of USA or UK rock artists. So its pretty hard to choose between them.
If you compare Australia to USA and UK, you would still say UK or USA, cause Australia had some great talent but there werent that many that became successfull overseas. I think mainly AC/DC, InXs, Midnight Oil and Silverchair.
By the way, Crowded House were Australian, they moved to Melbourne from NZ after the Split Enz broke up, who the Finn brothers were part of.