Back in August of 2011 I wrote a little utility that pulled down Alf Eaton's Album of the Year data. AOTY is nice for two reasons: a) I like Alf's taste in music, so the lists are relevant to me; and b) AOTY is a nice example of layering structured metadata into HTML, for easy processing (aka scraping). With the data in hand it was easy to to check to see if the albums were available on the streaming services Spotify and Rdio using their respective APIs. I was trying to decide which one to use at the time, and wanted to know if there was any significant difference in their catalogs.
Back then, it looked like 32% of the albums were available on Spotify, and 46% on Rdio. Alf has updated his list for 2012 so I decided to rerun aotycmp, and it appears that coverage of both has improved, with Spotify (41%) closing the gap a bit closer with Rdio (49%) which still has a comfortable lead. If you want the availability data I've updated it on Github.
I've been very happy with Rdio, although pieces like Damon Krukowski's (thanks @dchud) make me wish there was a better way to a) stream music while b) actually putting money in the artists pockets. I'd love to have the ability to pay a little bit more if I knew it was going to the help support the artist in creating more of their art.