I've been using spotify since it was available and subscribed as long as I've had a smart phone. So pretty much that. I'm a bit attached to it and even use it over free services.
I have tried Xbox Music, and it's not like I didn't think it was worth the money. It's just that I'm not going to pay for both.
I have to echo this, I used Xbox Music for a while but I just find Spotify much better. Xbox Music isn't bad, it's just Spotify is better for my needs.