I just came from a Blackberry Bold 9700, and while it served its purpose as a phone/messenger, the lack of everything else made it feel like it was ancient tech. The Blackberry Network that BBM runs off of is very unreliable though.
I recently went with the iPhone 4S and I love it. The apps are what really makes the phone popular. Messaging is getting better with iMessage, typing isn't as easy as on a Blackberry, but I manage. Email is a lot quicker than it used to be, maybe not as instant as it is on the Blackberry, but its still pretty quick. Everything is just a lot more simple on the iPhone. I am always worried about dropping the iPhone though, because of all the glass.
Good luck with your choice, both have their pros and cons, and I wouldn't count Android out of the race either.