Well, I've basically written what I have over an over at why I like WP7. All I can say is you need to run one for a week or so to "get it" and then you'll start to see why the interface is really the only way to go. This definitely applies if you're wanting to get things done with the phone and not just fart around with it because there's nothing else to do.
If you like games, spending time customizing your phone, trying out hundreds of useless apps just to say you did you should stick with Android or iOS. If you want to be cool like all the others because of the sea of useless "apps" then Android and iOS are the ticket! If you enjoy clearing out your text messages because your phone gets slow Android will rock your socks off
If you want to have awesome functionality, integration and speed WP7 is the way to go with zero slow down EVER. Most of the popular apps are on WP7 now and the sparse apps excuse is no longer an issue.