One way to measure the popularity of just about anything these days is the number of Google searches the topic has.
Music Business Worldwide looked at the number of searches for Spotify and Apple Music and found that Spotify beats Apple Music handily.
Except for a sharp spike around the time it was launched, Spotify (the blue line on the chart) has far more searches on a continuing basis than Apple Music (the red line).
That said, iTunes (the yellow line) beats them both, showing that the service still has plenty of life left.
Keep in mind that Apple Music is only 4 months old, and rumor has it that Apple is gearing up for a massive holiday ad blitz, which should raise the service's visibility significantly.