I really liked Google Play Music back in the day, especially the radio function that was a gateway/rabbit-hole into music and bands that I'd never heard before. I'd argue that it was my most valued subscription service of any medium. Then YouTube was bought by Google and they obviously wanted to only run one service and not compete effectively with themselves.
The problem, was they arbitrarily went with YouTube music and abandoned many of the great features that made GPM good in the first place. Playlists didn't migrate properly, the user interface was trying to be all things to all people and effectively was a rehash of the normal YouTube video interface, it all just felt forced and corporate.
Eventually, after a year of YTM, I gave up, found a 3rd party way to migrate my many, many playlists and album lists from YTM and moved to Spotify. Since then, I'll admit, if GPM came back, I'd probably not go back as the integration of Spotify as a native app in my cars infotainment system and with the whole-house Sonos setup I have would make it a downgrade in terms of lifestyle.
TLDR; long-term Google Play Music user, migrated when forced to YouTube music, didn't like it, Spotify is more user friendly IMHO. Plus, if your main use case is background/party music who really cares about purest HiFi anyway