For me, the iOS homescreen is too limiting. All an app can do is show its icon and a number of pending notifications. Android is too far the other way- widgets can be far too attention grabbing and obtrusive- silly animations of clouds moving in front of a sun, nonsense like that. WP hits a great balance between the two- widgets/tiles are of a fixed size, and the metro aesthetic means that none are too visually invasive.
I have a Windows Phone that I used as my primary phone for a few months before switching back to Android. The third party support wasn't there and the Maps functionality was dire. But I think that it has the best UI of any mobile OS out there right now- it's genuinely a joy to use. Getting Nokia on board looks to solve the issue with maps, and hopefully this codebase synchronisation will result in more third party developers making quality apps.
We'll see. Well, I won't, because my phone won't run WP8...