For me, Spotify was always the king when it came to music streaming. I was an early adopter, and I loved it - because it offered something new and exciting, in a whole different way. These days, my praise for the service has wained - there are several wolves at the gates and many of the canine contenders have nifty tricks up their furry sleeves.
I tried a few out. All operated on a similar fundamental level (same bitrates, catalogue sizes, price etc), but had distinct ups and downs when comparing useful features.
Spotify is still highly competent: it offers a huge collection, high performance delivery, and very good social integration (take it or leave it) with third-party apps extending the existing offerings. But I found that the radio service I previously loved was starting to churn out the same old stuff, and that the app hadn’t really advanced functionally in a long time.
As an Android user, I tried Google Music All Access first, finding that it solved all the problems Spotify posed, whilst taking away some of its good points. Its catalogue is massive, but it is unique in its ability to allow you to fill in the gaps by uploading your own music to the mix. Also, the radio is excellent - intelligent, fresh, and very well implemented. Furthermore, perhaps somewhat unsurprisingly, Google’s service offers exemplary Chromecast support - allowing slick usage of the little stick from both mobile and desktop devices.
Unfortunately, Google has poor social integration (it doesn’t natively interface with any other services, even Last.fm). There is no native desktop client, and while there are unofficial options (such as the plain-but-functional G-Ear Player and the Google-esque but currently buggy Radiant Player), there isn’t that uniform desktop presence that made Spotify so pervasive. It was also very difficult to migrate playlists from other services to Google’s.
In between Google and Spotify was Rdio, combining the positives of both of the other two services, but not doing either side as well. It has a desktop client, a good radio service, Chromecast support, and excellent social integration (better than Spotify’s). However, both the mobile apps and the Chromecast support are annoyingly unreliable. I couldn’t get the service to stream from my laptop, and while the stream worked from my phone it would frequently cut out. And most annoyingly, there is no “Play Next” feature, making impromptu party playlisting a very disjoined affair.
On the other side, Rdio (to me) looks the nicest. It has a very fresh and clean interface and and was a very easy switch from Spotify whereas the home-grown desktop clients for Google Music were a bit clunky. Rdio also has the advantage of offering a family plan - meaning much lesser costs for groups of 5 or less.
Basically, none of the big players are perfect. Spotify is popular but needs to be more inventive. Google has the tech but needs to play more nicely with others. Rdio is a pleasant blend of the two and cost-effective for groups, but is plagued by technical issues. You won’t be disappointed with any of them - just pick the service that caters best to your needs. For me, I may as well stick with Spotify - as I’m already invested in the service and old Spots can still throw its weight amongst the others. However, with the recent announcement of YouTube Music Key, it’s definitely worth keeping an eye on the Google camp.