Let provide some more details.......
Thanks guys for the replies so far.
340drv made the useful observation that I should really provide some more details about what I regard as a "good" trip. It's an adult trip, probably with two couples. We like scenery and staying off the beaten track where we can meet people and experience the US outside of the big cities. Typically we like to fly about every second day for 4-5hrs allowing plenty of time on the ground. So with 3 weeks I'd be thinking of a route of no more than 3,000 miles.
From the posts so far I'm thinking I need to choose either the "mountain west tour" or "gulf and eastern states tour". Both sound appealing.
1. Mountain West Tour. Say starting in Los Angeles heading east to the Grand Canyon and then north to Seattle then south along the coast back to Los Angeles. Is this something that could done in NA aircraft or would a turbo be needed? (In which case weight will be problem). The have been a lot of suggestions already about what could included in this tour. Any views as to whether this is done clockwise or anti-clockwise?
2. Gulf and East State Tour. The other option would seem to be an "east coast tour" including Great Lakes, Niagara Falls, Maine, Norfolk. Would the Gulf States be best avoided in September or is it more a matter of watching the weather and being prepared to change our plans? So far the scenery mentioned so far doesn't seem as compelling as the mountain tour. I assume there are controls for flying over Niagara Falls, how restrictive are these?
Any comments or suggestions on these two options will be warmly received!