well, which iphone are you going for...?
they both have their ups and downs....
i had an iphone 3G... was great fun for jailbreaking and getting themes and the like, but wasnt really that overall great because of the poor battery life...
i currently have a bb curve 8520, and i think its brill... i love bbm but the lack of really amazing apps is a let down, but i suppose the bb is more of a business phone than the iphone...
iphone has an easy menu, bb has a more indepth one
iphone cant legally transfer stuff over bluetooth, its awkward...
blackberry has this already built in...
its all down to personal preference.. if you can, go down to the nearest apple store and have a fiddle about with the iphones there... and then choose which suits you best :p lol
as i say, i cannot decide for you...only offer advice....if you like the iphone, then i guess its worth a try.. or if you prefer the blackberry then i guess bb it is

haha
hope this helps
ps, let us know which you decide mate

haha