Some of the similarities and differences between Google All-Access and XBox Music are discussed here:
Sounds as if Xbox music sucks on Android. But, it certainly doesn't on Windows/Windows Phone. None of the problems that they talk about are present. So, for me it's great - radio, playlists, unlimited streaming and download, collection match, etc. I supposed if I was using android, I would move to Google all access, but since I'm not - Xbox music works better. Not to mention, that it's library is about double the size of all access at around 30Million tracks.