A local dealer uses a Sonos system to conveniently access a vast library of music for equipment review purposes. The Sonos system is hooked up to MUCH higher quality DACs than that Sonos supplies. That Sonos server has access to the various download sites. Using this system, I like MOG for its pretty decent library of jazz and classical music, although Rhapsody is pretty good too. I haven't done much in the way of comparing the sound quality of the two services.
What is interesting is that even with the low bitrates of either MOG or Rhapsody, one can easily hear the difference between DACs used: better DACs mean better sound. It really pays to use better equipment even when the source is supposedly as limited as that of MOG and Rhapsody. At this dealership, we even shot out different DACs, including DACs that cost close to $60,000, and differences could be heard.