I'm going to start a bit of an argument here, but I'm going to be getting a new phone soon, and can't really decide which to go for.
I have had all of them in the past, and liked them all for different reasons, so I'm putting a poll on to vote for what you think is best out of Android, Windows Phone, Apple iOS and BlackBerry. When I check in a few weeks time, whatever has the most votes I will get.
Before anyone says it depends on what the spec is of each phone for how well it will run, I will be getting a reasonably powerful phone no matter which one I was to go for. I'm really asking about the software rather than hardware it runs on.
EDIT: If anyone posts a recommendation for Symbian, I will hunt you down and kill you. Its not on the poll as its so bad it doesn't deserve to be classed as a smartphone platform.