None

rsync like the NERD I am

Spotify. My CD library is uploaded to an old iPod Touch, which I listen to via the last.fm app (so it gets scrobbled). But nowadays, most of it's on Spotify (which can also be scrobbled), so I'll only use my iPod Touch if I want to listen something that isn't on there.

Spotify

No app, I have Android and I just plug it into my PC and drag and drop what I want to copy

I use iTunes and Spotify.

I don't listen to music on my phone. If I do it's probably YouTube. (Using Chrome, not the YouTube app). I might have Foobar2000 on my phone somewhere, not sure.

Plain old built-in iOS music app. Used to use Spotify before I decided to cancel my subscription and rebuild my own music collection (including CDs).

iTunes.