Hm, one of them is a service where you can listen to thousands and thousands of music with occasional interruption or for a nominal fee, you can download the music on your mobile devices or computer and there are no adverts. Also, you can purchase music and now you can use Spotify with all the music on your computer.
The other one is a service where you can purchase music and apps. That's it. You also need iTunes to sync your iPhone.
Never in a million years I would choose iTunes, which I think is a bloated corporate junkware.