I noticed that Google Play plays at 320kbps while Spotify plays at 128kbps (or lower). I don't splurge on $200+ headphones so I don't notice a quality difference, but I suppose some people can.
Google Play can be murderous to a data plan, but they also allow you to upload your own music. I don't think Taylor Swift is on a Google Play subscription either, but you can upload your mp3 and then have it available to you.