I would have been a heavy user of Google Play Music (free) just for cloud access to my complete music library on the go. At the PC I use MusicBee to play files locally.
But having recently gone through with the transition over the YouTube Music, I can say I'm so far extremely unhappy with it.
Just from a cloud locker point of view, they app has very poor usability compared to GPM. "Genre" is no longer a section and their "Artist" section only displays "track artist", not "album artist", which is a bit of a nightmare. Worse still, when you click on a specific Artist, instead of displaying albums you have by that artist (which every other normal player does), it gives you a long list of every single track by that artist. Totally unusable unless you enjoy playing random mixes of everything.
The other thing I found a bit disgraceful was that casting music through the app is now a premium only feature, which was free in GPM, though I believe they are looking into making it a free feature again.
For an app thats supposedly going to become the default music playing app on Android phones, I think its extremely half-baked.
I know I'm complaining about something Google are offering for free (cloud storage), but why downgrade the experience between two of their own apps?!
I think I'll be copying all of my music over to an SD card instead for listening on the go, instead of streaming.