I'm using a Galaxy S8+... the Samsung music player was generally fine, no issues with features or sound quality, however it has the same limitation with playlists that Google Play has, in that they can't contain more than 1000 songs. This is an issue for me because I have a playlist that has survived with me for the past 10 years or so with every phone I've ever had. When I get a new album, I listen to it in its entirety, but it's very rare for me to like all of the songs on it. Typically I really like 1/3 of the songs, kind of like another 1/3, and don't ever want to hear the other 1/3 of the songs ever again.
So as I play the new albums, I put the songs I like into a playlist called "My Faves", and I listen to that on random when I want to listen to music in general.
Problem with the Samsung player is that it won't let me add more than 1000 songs, which I ran into last month. So I went looking for another solution, and found Xperia music, which has none of the Samsung player limitations, and also is able to utilize the onboard Galaxy sound ehnahcements like UHQ upscaler etc.
Sound quality wise and with respect to other functionality I find the 2 players to be pretty equal, but the silly 1000 song playlist limitation is a huge oversight IMO, and for that reason I've relegated the Samsung player to the recycle bin along with Google Play Music.
Cheers
TRJB