Pandora has more songs than Last.fm, at least in the artists I enjoy most (often one album artists). I'm pretty eclectic though, and my opinion is entirely based on anecdotal experience, not statistics. Pandora has the ability to create separate "stations" and you can move songs to a different station if it doesn't fit the one you are trying to create. Pandora bitrate is higher too, I think.
Honestly though, I find Yahoo LaunchCast Plus (included w/ my dsl) has an even better selection. I also like LaunchCast's way of rating SONG, ARTIST, and ALBUM and creating MOODS which allows subsetting your rated music for specific occasions.
In the 2007-05-23 episode Veronica argued that Pandora and Last.fm wasn't really doing the same thing...
I'm only really familiar with Last.fm, and Pandora is not available for me to try anymore, so I have to ask:
What makes Pandora so different from for example Last.fm?
Does Pandora provide any functionality that Last.fm doesn't?
All I know is that it lacks the scrobbling functionality of Last.fm, and that it's unavailable for most of the world nowadays.
Is it that Pandora has a better selection of music available for streaming and/or have a better algorithm / better data for finding similar music?