Although honestly, that is subject to opinion. If you're the boring type who dislikes discovering new things or you enjoy the thrill of the hunt for new songs, then sure, Spotify is for you. If you like discovering new things, but you'd rather have the discoveries (that you'll enjoy) brought to you, rather than having to hunt them down, then Pandora is certainly a much better choice.
When I'm in a discovery mood, I take whatever song for which I'd like to discover similar songs and drop it into the "Moodagent" app in Spotify. It generates a list of 15-25 songs and explains the similarities for each, and I can promptly start whichever one I like.
Unless Pandora has substantially changed from the last time I looked at it, it had two big issues:
#1 - It had a tendency to get stuck in a rut. After a few hundred thumbs up and downs, it would decide to stop playing new music on a station and it would just give me songs I'd previously thumbed up.
#2 - It has very limited abilities to choose the music you want to listen to. It allows skip forward and backward, or to a different station, but no means of simply skipping the next 10 songs the way Moodagent within Spotify allows.
Plus... does Pandora have scrolling lyrics? The "TuneWiki" app in Spotify allows that.
Spotify is far superior to Pandora and iTunes - it's all the simplicity of iTunes coupled with the free of Pandora. Of course, that's just my opinion.