Not everyone uses every service equally, nor need the same from each service. "Listening to music" is a broad spectrum of activities in reality, and when I use streaming services, I almost exclusively use them for discovery and to find new music, and music I actually listen to more than once is bought rather than streamed. So while for me the single most important question for me is "How easy does this service make it for me to find new music?", for others, the question might be "What service streams the highest quality?". This is besides the whole legal thing with "What music is available there vs here" that others already mentioned.