There are a lot of music apps on my iPhone's home screen, and the reason I have so many is because I can't get all of the songs I want from just one service. I use Spotify to listen to new releases, SoundCloud for remixes and unreleased tracks, and YouTube for just about anything else that isn't available through the rest. If you're thinking that it's a pain in the ass to jump from app to app, you're right—but not anymore.
With the bop.fm Music Player, which is available online and in the iOS App Store, you can play music from Spotify, YouTube, and SoundCloud without ever leaving the app. Just browse through trending and popular songs on your feed or search for them yourself.
When you select a song, bop.fm will choose one of the three music services to play it with. If it's available on all three, it will choose Spotify first, since it has the highest quality tracks of the services available.
If a song plays through YouTube, the video will be shown along the bottom of the Now Playing page. You can even leave the bop.fm app and the song will continue to play in the background (a sort of workaround for the lack of a background-listening feature in the official YouTube app).
At the bottom of the "Now Playing" page, you can choose which service you want to play the song from (sign in to your Spotify premium account if available). You can also share the track you're playing, favorite it, and add it to a playlist.
Expect more music streaming services, like Beats Music and Rdio, to be integrated into bop.fm in the future. In the meantime, the three currently supported services definitely do the trick.