I would suggest using this app for youtube advanced premium version>
https://www.xda-developers.com/youtube-vanced-apk-root/ Its free and using since years..
It gives you lots and lots of premium features for free (fantastic must have app for YOUTUBE LOVERS)
spotify is 320 kbps ogg but people rate amazon music to be better in SQ than spotify.
Yes, Background play (you can still listen to your interesting stuff, while mobile is locked) + no-ads anywhere + black UI (videos look smarter in black background) + sound control via up/down swipe, these and few more are very interesting features.Why Youtube premium when there is youtube vanced? Background play and no ads.