Using Google Music just fine here. The battery life is staggering using it actually. I walk to work every morning ~30 minutes, streaming music the whole way and it's to bluetooth headphones. Typically I get to the office and the battery meter is still 100%, sometimes 99%.
Only downside is downloading songs is gimped. It seems iOS has no 'background' apps feature, so as soon as you close Google Music the downloads stop! Same goes for Dropbox, TripAdvisor, Spotify etc. etc. Really really stupid and infuriating!
Looking forward to the Nexus 6 now, so many stupid little things in iOS are starting to add up.