Since digital music is at the center of the music business these days, for essential for musicians to have a digital distribution company to get their work into digital stores, like iTunes and Amazon, and streaming services like Spotify, Apple Music, and Napster.
This article by Ari Herstand offers the most detailed comparison that I've read anywhere. Digital distribution is not a one-size-fits-all proposition. So it's important to do your homework to find the best company for your needs. That can be difficult because some of the companies don't disclose all of their fees up front. It can also be hard to understand exactly what services they offer.
Ari's article is a great place to start your search or to compare what you already have with other options out there that might work better for you.