Spotify is way ahead of Apple Music on everything to do with discovery. I tried to switch to Apple Music (mostly for the Homepod Mini support) and really disliked the apple music app.
I have a suspicion that if I'd actually paid for Spotify and stuck with it for a few years, though, the reverse would be true. My gut feeling is that these two services just aren't different enough in practice to make switching between them worth it for most users, unless they want a feature in the larger ecosystem (e.g., AirPlay 2 or Spotify Connect).