I'm not sure how it compares with the Iphone since I am a Droid User. But I have compared the Droid with my Garmin nuvi 250w. My 2 cents is this…
The Droid uses Google Maps to give directions, so I would think this is a little more current data then the Garmin maps that get updated once a year (if you choose to pay the $80 to do so, or know how to illegally update them). This is nice when you’re out looking for a place to stop to eat or another point of interest. On the other side the Garmin is VERY easy to use, and comes with a Window Mount, so I find myself using that more so I can glance over it at. I can get the directions in faster with the Garmin and be on my way. The Garmin also has a bigger screen.
So I still use the Garmin as my primary GPS, but that may be because I had my Garmin before my Droid and I am used to it. I also don’t know how much you drive, I’m on the road a lot for work. I would try the iphone 1st and see if it suites your need. Then you can see if you want something more.
