Since RIM is circling the drain as a company you’re better off deciding what you want the phone to do, and then picking an OS whether it’s Android, iOS, or WP8.
You’ll only get the most out of the iPhone if you already run an apple ecosystem. Android has almost caught up with iOS in terms of apps available, and offers a fair bit more flexibility if you like tweaking and fiddling. WP8 is still lagging behind in terms of app store ecosystem.
It really depends on your usage and preferences, there’s not clear cut winners and losers any more.