I use Amazon Unlimited and Apple Music. Amazon Unlimited has more music to choose from and works with Alexa if you use that. Apple Music is integrated into iTunes and your playlists get propagated to all of your devices using iCloud. They both sound identical to my ears. Differences in sound quality are most likely due to different mastering, not the compression by the streaming service.
Spatial audio is more of a useful feature if you have a 5.1 speaker system and AppleTV's set top box. It isn't terribly impressive on AirPods yet. It sounds good because of the better mastering, but not spatial.
Beyond the way it works with the audio equipment you have, choosing between the services is more a question of whether the music libraries there are good for you. If you have mainstream tastes, any of them will work for you. If you listen to classical music, you might want to go with Primephonic or Idagio which specialize in classical music. If you like vintage music, like classic country or early jazz, Amazon Unlimited has the biggest selection.