Amazon’s mobile app has a clean app interface and simple layout, but it’s awful on the web. Voice assistants have made these apps less important, because you can just ask for whatever you want, but services should spend more time improving their apps.
A music service only works when you can use it. In that sense, your choice might already be made for you. Got an iPhone and thinking about a HomePod? Get Apple Music and use Siri to control it. If you’re an Alexa household, Amazon Music works best. If you’re starting from scratch, Spotify’s the way to go: It’s practically ubiquitous across devices including Amazon’s Echo speakers, and the Spotify Connect feature makes it easy to control what’s playing—and where—from within the app.