Forbes Online has posted a rather brief but mildly interesting matchup comparison between Apple's popular iTunes Music Store and Roxio's Napster. The report does however give some insight into the popularity of online music, and the number of users actually using "legal" music downloads.
I haven't given Napster a great deal of consideration, but from what I've seen of it, both the software and service could use some improvement. I'd choose iTunes over any other existing online service any day. That could change though when Microsoft enters the ring later this year, or early 2005.