This question is often debated but never resolved. unfortunately when the marketing machine for both blackberry and apple kick in its makes choosing a device a lot more difficult.
if you are only concerned with emails, calendar and contact management, the blackberry wins hands down.
if you travel alot and like music, applications, want to check where to eat etc , then the apple is the winner.
overall there is not much between both mobile phone systems . i would always choose an phone based upon, speed of access to applications, speed of internet and ability to interface with my office desktop.