To me, it's not a simple matter of better or worse. When you measure of pure specs and stats, Windows Phone will be better at X, but Android will be better at Y, and iPhone will be better at Z. In my opinion, it's a matter of overall experience. To that, Windows Phone is my favorite. The user interface provides a great overview of the data you want to see on your phone, as well as almost always looking clean and fluid and consistent across different apps and phones . I think Apple's and Android's recent emphasis on UI have come as a result of WP. The core of the operating system was well optimized to run on smartphone environments, even with low powered ARM processors, the performance is generally very good for the OS itself.
The overall result just makes a generally enjoyable and satisfying mobile experience. It isn't always easy to show in commercials, and it won't make your friends jealous, but it's why I continue to use Windows Phone.