I prefer Google Music. Having it all in the cloud is so that I can decide what I want to listen to at any time is too convenient.
Also very easy to cache albums so that you don't always need an internet connection or to use data.
It's a bit of work to get it on your phone but doesn't require rooting or anything like that.
http://www.engadget.com/2011/11/19/h...e-of-the-unit/