I'd be interested to know how many people pay for streaming music services. I use Pandora, but just the free version. I would think with cell phone carriers getting rid of unlimited data, streaming music on your phone isn't as appealing as it used to be. But I could be wrong.
I subscribe to the Spotify service. At the time I started, Spotify on a mobile device was only available to Premium, so that's how I got started.
Spotify has the ability to flag playlists or albums for offline usage, so I have a few playlists with several hundred songs that are always on my phone. It's really easy. After years of hoarding MP3 files, I never bothered loading my latest phone with any MP3 music and use Spotify exclusively and I haven't missed MP3/itunes for a second.
I used to use Pandora and if you just want to put on some 80s music in the background or what not, it's pretty good. If you want new music or have the desire to listen to album ___ by artist ____, Spotify absolutely crushes Pandora.