Pandora vs last fm

Best thing will be to combine both of them,they actually work pretty well together.
Pandora is great when you know an artist or a song and you want to hear something similar. last.FM on the other hand has a very large library of bands and artists-all are tagged,briefly described and most of the big ones even have a samples.

The big advantage of Last.FM over Pandora is the tagging system that allows you to discover music by genres and not by providing a similar artist.

 If your are in it for the radio then better stay with Pandora. last.FM's radio is nice but it pales in  comparison to Pandora. the only advantage of last.FM's radio is that that you can listen to a radio station by genre.

I was on Last.fm over a year ago. Then, I made the switch to Pandora. All I know is that I never looked back. Pandora.com probably seemed superior to me because the new music or associated music is based on a complex, music-based algorithm, rather than the "other people who liked that also like this", collaborative filtration approach. I agree with Areh that you cannot select genre explicitly on Pandora. However, I have found choosing a few artists or songs that you love in a particular genre will produce wonderful music that satisfies your current mood.

I think you will find Pandora will more accurately fit your tastes! 

You might also try Musicovery.com - it creates dynamic playlists based on your mood and genre selection.

I prefer Pandora quite a bit.