You mean where are best compositors live? I think they all around the world. For example Jesper Kyd live in USA, and Vangelis live in Greece. They both my favorite compositors. If you talking about music brands like 50 Cent or Shakira - at this point of view USA is the best country, because it provides more opportunities for musicians, like a lot of sound-studios and investors. But offcourse all new labels are statring theyer way to fame from their local studious. But if we will be judging about country's musicians by counting how many new labels it have, will be only counting new labels nothing other. I guess the proper mark of countrys music opportunites would be a count of acting labels and as i say earlyer its USA.
PS: In our language we have some kind of Idiom for this kind of questions:
"There cant by any disputes about tastes". :)
For me most of the world music is just a trash, i can't even imagine that i would be listening it. I cannot determine where are from these musicians i like, but mostly of them, i think, are from USA and Great Britain. The music style i like are name New Age.