I personally like Slacker better than Pandora, for a couple of reasons. First, the playlist is better on Slacker, secondly I think the audio quality is better than Pandora. One of the huge benefits of Slacker is also the fact you can cache stations, however it has to be the Premium now. Back in the dark ages when I had Blackberry phones, Slacker allowed you to cache with the basic subscription, and I really missed that a lot.
So, today I got an email from Slacker saying if I signed up on Facebook I can get a free month of premium. I jumped on it, and now am caching 6 of my favorite stations. I wanted to give everyone a heads up about this.
Just go to the Slacker Fan Page on Facebook and enter the promotion. It's really simple.