The rendering speed of the N1 amazed me the first time I pulled up a page. It also has enough RAM to keep more than one page open at a time without having to re-load as you switch windows (as I discovered with the iPhone). This may have been addressed somewhat in the 3GS but I only had a 3G model.
I also appreciate OTA syncing for contacts and calendars that doesn't cost me $100/year.
The integration with Google Voice is also a plus (having it auto-switch your voicemail over, and make all outgoing calls through your GV number).
Disclaimer: I've never tested the call audio quality on any model of iPhone, so I can't make a direct comparison between the two. I can say that my N1's call audio quality is far better than on my old Razor (both on Tmobile).