At the time of writing, Apple Music and Amazon Music Unlimited have the largest catalogs with 100 million tracks each, followed by Spotify with 82 million. But that's not the end of the story: The number of songs offered by a music service used to be the main differentiator, but as always, it's quality over quantity that counts -- and particularly if you're looking for more obscure tracks. Depending on your favorite genre, some of the services may offer a better catalog for under-the-radar (Spotify), indie (Apple) or hip-hop artists (Tidal). Users who are less ambitious about expanding their musical taste should be satisfied with the catalogs that all the services offer.