I had a Blackberry and loved it. Upside: it did everything I needed and more. Downside for me: I thought the OS was a little tricky to get used to until I figured out how to run it. I didn't feel like everything was intuitive I guess.
Now I have a Motorola Droid and I love, love, love it!
It does everything, there are tons of free apps for it, it's FAST and pretty user-friendly.
Have fun deciding!