Also, I have a Pandora account, but I really have never used it. I liked Slacker better at the same time, so I set up a great playlist mix of over 100 artists, and I just start it playing, let it do it's thing, and just enjoy the music that comes out.
But, Amazon has not set it up on Echo, so what I do is get Slacker playing on a mobile device and then, via BT, I can play Slacker to most anything -- including Echos, of all three flavors. Works for me.