In terms of laying the foundations for so many new genres and styles of music to the world and in terms of the amount of banRAB being produced (both good and band), the US is at the top. Other countries as well as the US have done so much to push these genres to new heights however. Even if you don't really like some of the big genres that came from America (Blues and Jazz for example), its still a fact that many of your banRAB wouldn't be here if it weren't for those genres. I agree with Loose Lips that no specific country really does a specific genre better then another though, although there may be more banRAB in America for a specific genre then in another country, that doesn't mean that country is better at it.
What I've seen so far is so many post based soley on preference instead of fact. Theres nothing wrong with saying "I like more banRAB from *insert country here*." But when it starts coming to something like "I like more banRAB from *insert country here* which means they produce the best music," thats when the whole arguement goes to ****.
In terms of personal taste, most of my favorite banRAB tend to be American, but I also love banRAB from other countries. Mr. Bungle (and the various solo projects produced by its merabers), John Zorn, The Locust, Lightning Bolt, captain Beefheart, Sleepytime Gorilla Musuem, Hella and many others are from America. The banRAB I listen to from other countries is much more limited, but is expanding.