You're comparing apples (or Apples) and oranges with an iPhone vs. Blackberry. Two different functions, optimized for different purposes.
I used to have a Palm and switched to a Droid-based phone (Droid Incredible, then the Droid Incredible 2). So unfortunately I can't specifically compare the iPhone to the Blackberry. But if I were looking for a smart phone now, I'd go with either a Droid or (based on recommendations from some of my friends) an IPhone.
If I were looking for something to do presentations on, I'd look at either an iPad or a Droid-based device. As Dan points out, one limitation of Apple devices is the inability to run Flash. You'd have to consider whether that'd be a deal-killer for you.
Another option is a laptop, depending on your needs. And there are some devices that function both as tablets and (by hooking it up to another device) as laptops. Asus, for instance, makes some with good reputations.
But the first question really is: What are the primary functions you need it for?
Hope that helps.