According to the 2014 edition of Edison's annual audio report "The Infinite Dial", Pandora remains the most popular music streaming service in the United States. 31 percent of those polled for the report stated to have used Pandora within the last month. That puts the ad-supported online radio healthily in front of iHeartRadio and iTunes Radio which were used by 9 and 8 percent of the respondents, respectively. Ranked fourth, Spotify was the first on-demand streaming service on the list with an adoption rate of 6 percent.
There is only 1% separating iHeartRadio and iTunes Radio; however, Apple has quite a way to go to overtake Pandora.
Check out the chart below for more details...