Spotify was a bit buggy on my laptop a while ago so I stopped my premium plan.
I used the excellent soundiiz to transfer my playlists over to youtube (in small 200 tracks batches), where I had a premium account.
The thing is, youtube music uses the videos as audio source, and artists often add noise to the video clips to make the "listen for free" youtube experience inferior to buying a cd.
And I end up paying to listen to this crap.
Edit : the "mix" feature tends to mostly play songs that are "clean". It's more my imported likes that have the added noise.
I actually kind of like what youtube is auto playing, and I've discovered a few good new tracks. For the price I pay (~3€/month, i'm still on a Russian plan =D ) I'd say the service quality is fair.