Compared to things like bicycles or shoes, music subscription services are remarkably undifferentiated. They all have more or less the same selection of music, and it's generally available for the same monthly prices: $5 for listening on a computer, and another $5 to add mobile device(s).
But in practice, several factors and details offer music fans some degree of choice between the big five, should they decide, in the manner of our early ancestors, that they're ready to quit hunting and gathering for downloads and free streams and hunker down to the "agriculture" of a monthly music subscription that can sustain all of their musical needs without requiring nearly as much legwork or incremental costs.
If you're ready to move past paying for digital downloads and foraging for whatever you can eke out of MP3 blogs and YouTube, check out these reviews of the big five cloud-based on-demand music subscription services to decide which one best suits your needs.
These reviews emphasize the mobile experience, because today's smartphone apps make portable music subscriptions far more attractive than they used to be. We declined to rank them because what might be right for you may not be right for some. Here they are in alphabetical order:
Update: As early commenters have pointed out, Grooveshark is another option. We didn't include it in this round-up because both Apple and Android pulled Grooveshark's mobile app from their app stores.