I have an Amazon Prime Membership which gives me access to a fair amount of music, and I have also been considering Spotify and Google Music.
One of the things that annoys me about all the services I have tried, is that I am unable to specify which music output device I want to play to, such as my airplay devices etc. It seems especially poor for Spotify which is an actual app.
I can work around the problem somewhat by changing my default output device if I have headphones attached via USB, but as yet I can't find a reliable way to airplay my music.
Anyone else have any general comments re Spotify vs Google Music?