Pandora usage is still far more common than Spotify use. Edison Research and Triton Digital found in February 2015 that 27% of US consumers listened to Pandora, vs. 7% who used Spotify. And November 2014 research by RBC Capital Markets found that 51% of US internet users used Pandora, vs. 14% who used Spotify.
Overall, the music streaming industry is booming. In March 2015, the Recording Industry Association of America (RIAA) reported that US streaming music revenues increased about 29% last year to reach $1.87 billion, accounting for 27% of total industry revenues. Read the rest at eMarketer.