I personally just use local music playback, with SyncThing for syncing between devices. That mean I can listen to them offline!

On Android, I use Auxio, but Lotus and Chocola (previously CuteMusic) are awesome too.

On Linux, I use an mpd-based option called rmpc. Tauon and Gapless are also great! As for mobile Linux, Gapless is a good option that works pretty well. You might also like Plattenalbum, a GTK-based MPD client.