I have used iOS in iPod Touch 4th gen and currently have both the Nokia Lumia 920 as well as the Samsung Galaxy S3.
UI :The Metro UI with the live tile of WP8 is simply mind blowing. It is beautiful, fluid and fast. The UI of Android looks more or less borrowed from iOS. The animations while opening, closing and browsing within an app makes the experience awesome in Windows Phone 8. As an example, both Wikipedia and Urban Dictionary have official apps for Android. Yet, the unofficial apps in WP8 look much more pleasing. The live tile feature keeps you more engaged and prompts you to open the app. The live tile is also useful in the sense that I can see a new word daily right on my home screen.
Apps: This is one area where Android beats Windows Phone 8 hands down in the sheer number of apps. That said, Windows Phone has all the useful apps. So you won't get stuck on a job because that app is not available except perhaps Instagram. But it has many alternatives like lomogram, Fantasia Painter, #2InstaWithLove, Sophie Lens, etc. And none of them are bad at all.
Office: WP8 has great Microsoft Office Integration enabling you to access and edit your stuff on the go.
Notification Center: WP8 lacks a unified notification center like Android. It is very useful and this is really missing in the OS. But Liquid Daffodils is said to be bringing a notification center soon to the platform.
Google Apps: Google apps like Google Now, gmail, youtube, etc are truly awesome and are prominent by their absence on WP8. However, the navigation apps of Nokia (HERE maps and HERE drive) are right up there with Google Navigation and in certain features like offline POI's and Speed limit alarm outperform the Google Navigation app. In terms of reliability, I weigh both equally since I have never been misled by either.
Closed vs Open: The ability to root your android device throws open a world of opportunity for you to tweak the OS. You can install custom ROM's, overclock your CPU and even install custom kernels. This is not possible in the closed Windows ecosystem where you are restricted to the Windows Phone Market for your apps.
Innovative Features on WP8: The kids corner and the rooms features in WP8 are very original and innovative. They have no counterpart in Android. The integration of the people hub with Facebook, Twitter and all other email accounts saves a lot of time and you can get all updates about your friends at the same place. Also, you can freely transfer contents to and from WP8 like a USB drive without having to go through Zune.