I have just read an excellent article about the differences between Pandora and Last.fm. Both, as you know, are services that gives you a radio stream with musics selected for you, that is, a personalized stream. But they are totally different in the way they select your musics, and that difference is the inspiration for this post title.
Pandora uses a nature approach since Pandora's recommendations are based on the inherent qualities of the music. Give Pandora an artist or song, and it will find similar music in terms of melody, harmony, lyrics, orchestration, vocal character and so on. So you will get similar musics, or as Pandora likes to call it, music with similar "genes".
On the nurture side (as in, it's all about the people around you), Last.fm is a social recommender. It knows little about songs' inherent qualities. It just assumes that if you and a group of other people enjoy many of the same artists, you will probably enjoy other artists popular with that group.
The article brilliantly explains the differences in these two different approaches, as some of the problems that can occur in each other. It ends with some results for different tests the author has made, it seems Last.fm is better.
Click here to read the full article