It depends what you want it for. iPhone is better for personal use, while Blackberries are better for business use.
Well, it's not that simple. If you want a great platform for applications and occasionally the need to send/receive emails and phone calls, then get the iPhone. Otherwise, the BlackBerry is head and shoulders better (i.e. if you rely on a phone or need to get email anywhere and it all has to "just work"...then BB it is.