I much prefer the UI and it (used to?) allow uploading my own music where the offering was lacking. Notably, Spotify also didn’t have these songs, so having them in one library is great. The recommendations are also spot on for me, but like you said that could be attributed to having used it for a long while (used Play Music pretty much from its inception).

Considering I’d want to pay to get rid of ads on YouTube too having the music service bundled is a bonus. I used to pay for the music service standalone before that.

I bet that Spotify will do just fine now, although last time I tried (some time last year) I didn’t immediately like the UI, and the shuffle seemed to work oddly in large playlists.