Slacker Radio Premium
Between Slacker and Pandora, and I pay for both, I prefer Slacker. Slacker allows you to fine tune your station, like more deep tracks, play songs I've rated more or less often, that sort of thing. After making myself more productive listening to Pandora and Slacker for hours at work, I think Slacker has a larger library too. I don't get repeats as often with slacker as I do with pandora. However, Slacker needs to get it's arse in gear because Pandora pretty much owns the network appliance market - if you buy a new tv or bluray player, chances are that it'll have Pandora support and not Slacker. Since I'm a hevy music user, I still pay for both for that reason. If you're only listening on your iPhone or computer and had to choose one, I'd go with Slacke for the aforementioned reasons. Not that there's anything wrong with Pandora....