The US has wonderful scenery and the airspace system is wonderful to fly in. The Midwest is extremely boring though, so I'd choose an area outside of that. During September, the NE, Great Lakes, Rockies, PNW are all beautiful.
One thing I'd like to emphasize though as a Colorado resident - if you chose to fly in the interior of the Rockies - make sure you have both pilot and plane wired tight. Four adults plus gear in most Cessna's isn't going to get it done for a lot of our mountain airports and their surrounding terrain. There's a lot of 14,000' chunks of cumulous granite, and if you're a flatlander - performance degradation from a book perspective to the real-world perspective will be an eye opener. Make sure you leave yourself a LOT of safety margin. That being said, on a nice day - there's not much finer scenery to enjoy out the windows.
Where ever you end up flying, fly safe and enjoy.....