I'm bumping this because I've come to a revelation:
Slacker > Pandora in almost every way.
The NEW Slacker anyway - a lot has changed in just the last few months.
I have been growing increasingly weary of Pandora, my preferred music-streaming service for several years. In 2008, I tried out Slacker and hated it - the interface, the commercials, the clunky intrusive ads, and - most of all - the limited song and artist seeds available to non-pro users. Pandora was clearly better for the non-paying customer and the service was solid and reliable.
I spent literally years tweaking my station. Thumbs upping, a lot of thumbs downing, adding songs, removing songs, artist additions and subtractions, more thumbs up, more thumbs down. I grew to hate it. I found it wasn't playing the type of music I was really looking for (best not get into that). Some songs it would play ad nauseum, while others I thumbs-upped never at all. It came to a head when I bought a new car and got satellite radio 3 months free. Wow! Did I get exposed to lots of great new music that fit the genre of what I was trying to "discover" but never got played on Pandora (mainly from Alt Nation and XMU). It came to a point where it was either pay for XM or go back to Pandora, a prospect I was not looking forward to.
Then someone suggested I try Slacker. I scoffed at the idea, I hated my brief experience with slacker years before. But I decided to try putting together a station.
First of all, the canned stations are already fantastic. It's already like having a whole XM station selection, minus the annoying DJ's. It has the same song and artist seeds that you can put together on Pandora, but one of the greatest features is "fine tuning." Sometimes, if I really want to discover NEW music (as in recently released) I can tell my station to play recent stuff. If I want to dig a little deeper into older stuff, I can do that too. I can have it play just familiar songs, or I can have it go into more of the B-side stuff. Not only can I ban individuals songs, but artists too (a great feature). The service seems more reliable that it previously was, and the ads less intrusive (no more so than Pandora, who has really kicked up the ads recently). The mobile app for Android recently upgraded and it's pretty nice - you can quit the app, you can do a lot of fine tuning within the mobile app itself, and I feel like navigation is easier and quicker. Plus you have the option of caching station songs to avoid buffering in areas with lousy coverage. Plus the bluetooth streaming is less of a headache than it was with Pandora (maybe that was just me or my devices).
In a recent web app update, you can easily put in song requests filtered by artist (awesome!) and even play individual songs from a list of songs that haven't played on your station lately.
All in all, I've only scratched the surface, but at the end of the day, Slacker has a larger music library and far more customization. If Pandora is playing the songs you want to hear, then maybe it's perfect for you. But I think Slacker is better at playing the songs I want to hear, playing less of the songs I don't, and discovering music similar to my actual music tastes - not just what has a similar music "DNA."
Pandora is done, I'm switching to Slacker permanently and - even though the premium version costs a bit more - I'll probably splurge for that too. It's still cheaper than XM.