If you plan on doing a lot of typing, the Iphone might not be the best for you, many people complain about the size and accuracy of the virtual keyboard. It has the best mobile browser, so for surfing it's unbeatable.
Both devices have an app store, that offers many games and apps to meet your needs.
I prefer the Blackberry, because for me, a handheld is supposed to be utilitarian, and I like having an actual keyboard. Furthermore, you can replace the battery yourself without having to get the device serviced, since the Iphone's battery is built in. Furthermore, setting up email on the BB is much easier than on an Iphone, since it's done online through the Blackberry Internet Service, as opposed to setting it up on the device itself.
You may want to hold off on making your decision till around Xmas. The Iphone 3Gs is the most solid offering Apple has, but RIM is coming out with a 3G BB that will have a keyboard and a touchscreen, which is what I'm waiting for.
However, if you already have a Mac computer, the Iphone just adds to the Apple Experience.