I've never compared Spotify to Amazon but when I was comparing Tidal vs Qobuz vs Deezer vs Spotify (and it was quite some time ago, probably about two years ago or so) not all of them had the same volume level: some services were a bit louder than others, so were sounding "better". I don't remember which anymore, too much time passed. Out if these four, Tidal had a horrible app, Qobuz - horrible catalog (half of the songs missing) + bad app, Deezer - good catalog and decent app, except for the fact that smartphone app was VERY buggy (main issue was that it was just randomly stopping and not resuming playback if Internet connectivity was not perfect, so basically it was never working properly on the move). So, Spotify it is... Otherwise it would have probably been Deezer.