I now have both phones. This isn't a totally fair comparison, as I have a NEW Moto Droid, and a 1st Generation iPhone.
The iPhone is definitely a great phone, that redefined what should be expected from a smartphone over the last couple of years. The apps that are available are excellent. The usability of the device is incredible. The interface is Apple shiny smooth. The call quality is decent, and the media capabilities of the device are unmatched. The exchange integration is mediocre at best, and the first generation's lack of hardware encryption makes it almost useless to any corporate user due to prevalent mobile device security policies of the day. Where this phone fails, is the network. Yes, my phone isn't 3G. It doesn't matter. AT&T 3G coverage in my area is spotty at best. Why would I upgrade to pay $10 more a month, lose my text messages, and get the same data speeds?
The Motorola Droid on the other hand is almost the opposite of the iPhone. The Droid runs Android 2.0. I am very impressed with the Android OS. It does a lot of things extremely well. It also fully supports Google Voice, which I use almost all the time for inbound call screening. The best part of the Droid is it's network. The Verizon 3G network has yet to let me down in the many, many places that I have taken it. The corporate email is still lacking, as it doesn't have a full implementation of ActiveSync. No remote wipe, etc.
To get around the corporate issues, both of these phones are supported by Good Technology.
So, the deciding factor for me on this, is the network. AT&T is totally spotty when it comes to 3G. You can't dual task on the phone in Edge mode. My suggestion, get a droid and an iPod touch.