I have been a user of the three. Slacker is great! Its free service plays ads but, it's mixing capabilities are just beyond of Pandora's... which usually follows a very marked pattern of song genres. Pandora, however, has no monthly or daily limits, as Slacker has. Spotify, on the other hand, was great when it started. You could pick your song like it was a Music Vault, would play whatever you asked it on demand... but then, the Facebook thing came along, and then I went overseas to Puerto Rico and it started complaining and asking me to pay if I wanted to listen again. At the end, free music.. some ads... no limits and can listen everywhere.. Pandora WINS!