I know there are different use cases for each, but generally do people prefer self hosted nextcloud, proton docs, or libre office?

No, development is still stalled. You need to pay if you want the really high bit rate flac downloads. I pay and can use Deezer as a backup to Jellyfin in the event there’s a song I don’t have and I’m driving. I was looking at music fab, but it’s expensive, the Spotify downloader has worse quality, and doesn’t grab the cover art, which is probably a deal breaker for me.

I use the former. How does it compare to the other two?

Are they on Deezer? If so, look into deemix-gui.