This article from Lifehacker sums up online music purchases well. I actually have used and continue to use all three and agree pretty much with everything in this article. I used to buy everything through iTunes but now buy my music through the amazon store and then import them to iTunes because the music is usually about 10-30% cheaper on Amazon MP3. Check out Amazon Music here
It’s a great article to get you up to speed.
Google opened its new music store to all comers in the US this week, touting its partnerships with music labels and indie musicians, and its broad reach thanks to the Android Market. The new store has millions of songs for sale, but whether it’s a game changer, serious competition for iTunes and Amazon MP3, or the best online music store out there is another question entirely. Let’s take a look at each service based on its features.
Each music store is a little different. This showdown is all about the music stores that these companies offer—not their respective players, applications, or services. We can’t help but mention them in terms of usability and integration with the store and the user experience, but we’re going to try and focus on the features of the stores and steer clear of the bugs or quirks of each player.