Personally, I have not used Windows Phone..
Nokia Lumia 710 has good features.. Nokia is a stable phone and now comes with Windows Phone 7.. that combination will be better than Nokia-Symbian combination.. No other Windows phone may create an impact the way Nokia is going to create..
Android is the best OS except for the battery issues.. Android 4.0 (Icecream Sandwich) will be launched early next year.. The various manufacturers are listing the devices to get Android 4..