There are many developers that spread themselves over multiple mobile platforms. In case you are not one of them and need a comparison between the three major ones, here you go. This article explains some basic differences you'll experience when dealing with iOS, Android, and Windows Phone development.
Here is my take on the article
iOS is still the best and most robust development experience, and they have stable documentation that can be easily demonstrated through examples.
Android is fragmented but still pretty decent when using Eclipse with Android Java embedded. Android's biggest hurdle for any developer is the unpredictable nature of your app on top of a particular OS layer / device combo (fragmentation).
Windows Phone is still pretty young to give it a fair shake in my opinion because they are still refining the overall process. I will point out though, it seems a bit clunky to me having to deal with workspaces like Visual Studio and building objects in a object oriented fashion (optional).
Take a look deeper into this article though for some more technical differences, especially in the API's.