MP3 Downloads: Amazon or iTunes?

"...I heard a song that I liked a lot.... The next day I was thinking to myself that perhaps the rest of the album was worth getting.... So I went over to iTunes I saw that it was available for $9.99.... [But] I... discovered that it was available on Amazon.com for a good bit less...."

Dan Cohen at GearDiary has done a small comparison of MP3 album prices between Amazon and iTunes. His article points out some interesting differences between the two sites, such as albums having differing number of tracks, which certainly surprised me! He concludes that Amazon was the less expensive retailer, at least for the titles he compared. Frankly, I have never downloaded an MP3 album, as I still prefer a "hard copy" (a CD, or LP...), but for those of you who have, is Amazon or iTunes your vendor of choice? And is price the only important distinction between the two? Or are there other retailers which offer even better bargains or other advantages?