When I use an iphone, the sheer lack of a back button to close an app when you are done using makes my brain hurt. The way you have to bounce back to the home screen, then open a task manager feature with a double tap. That is very very annoying.
Android is a whole other mess. Fragmentation, poor performance and more plague Android. While the newest generations of Android phones are getting better, I still just don't like the options.
Blackberry is something that I haven't really looked into much with the BB10. I think that there are bad times ahead for them...
This makes it sound like Windows Phone is just the least bad choice, but I don't consider it that way. I just really like the way the core OS operates. I like the concept of the hubs, even though it never quite worked out the way Microsoft had intended at the beginning. I really like the big informative tiles that display relevant information...if you were to look at the list of apps I use on a daily basis, it would not match how I use the phone. I use Weatherbug every single day, but I haven't launched the app in weeks.
I think WP8 got a big boost with Nokia and it's user experience. Their phones are just very well built, good looking phones. And their apps, like turn by turn GPS is just fantastic.