Idk. I can't decide. Something about the idea of 4.5inches is really appealing. For ebooks, videos, graphics, etc. You accomplish a lot more. Like that recent
Googlesearch iPad app. that wouldn't work on a 3.5 inch screen, but something pretty similar COULD be done on a 4.5inch screen. I REALLY like the idea of relying more heavily on graphics/objects for touch interfaces rather than scrollable walls of text. More real estate makes that a much more realistic prospect.
HOWEVER, I actually just lost .2 inches in screen size going from the Droid to the iPhone. And couldn't be happier. Since the AR is wider, it actually "feels" bigger. I think 4inches even might be the sweet spot. I don't know. I think something larger has a multitude of benefits that probably outweigh the slight extra girth.