FYI – the new (legal) Napster is out. I did the early sign up so I could get the 5 free tracks (an offer they had out a few weeks ago). As I said before, I've also signed up with iTunes and had been really happy with them – however I personally think Napster might have iTunes beat.
Buying music was certainly error free with iTunes, but the interface is a bit clunky (something I would expect better of Apple). I just had an easier time searching, buying etc. for songs on Napster. I could go into more depth, and I'd probably have to play with it a lot longer to pinpoint what it is I like more about Napster than I do iTunes, but those were my initial impressions. I just felt more comfortable in the Napster interface. One thing I WILL give you is that it MAY be because many of the GOOD things I liked about iTunes, I saw in Napster interface.
One thing I still have yet to do is BURN A CD with Napster. (This was accomplished, again error-free on Apple's iTunes, and was only impeded by what I think was bad interface design). But based on the ease of purchase/download etc. I'm not expecting any issues with Napster's burning ability. (Not like I did when I purchased/downloaded music from buymusic. With this much REALLY GOOD competition between iTunes and Napster, I don't picture buymusic lasting too long)