I've had a WP7 Mozart for the last 2 years and the OS is great to use, and far more user-friendly than both android or whatever apple call theirs these days. WP8 is even better. Depending on what WP7.8 offers when it gets released, I'll either stick with the Mozart or upgrade to a WP8...either HTC 8x or a Lumia 920.
Form what I've read - if you want a good camera get the 920but it you want a great MP3 player go for the 8x