I had gotten Youtube premium and enjoyed it. My subscription ran out and I find I have 90% use of it for free. I got it to listen to the app on my phone when I was out. However the app sucks ass. I would listen to one song and then the app would just crash. SO I never got to use it for the intended use.
So which would you choose? Youtube or Spotify? and how is the Spotify app on the phone?
Spotify app is OK. I can listen to music on background with no problems. You said you listen to obscure songs, Spotify is lacking in that regard and YTM has the best library.