We have a 25 foot Dutchmen and have traveled a quite a bit. At Glacier National Park spaces were limited, even PUPs were tough in spots. But in general this is rare.
Out West many of the campsites are smaller but that doesn't stop them from packing rigs in like sardines.
Usually were able to avoid such problems but once or twice we just had to tough it out. Of course we were gone most of the day sight seeing.
In the end you pick the floor plan you like, our floor plan included the ability to wind through city streets and find quilt and gun shops. For us that was 25 to 28 feet.
Rent the size TT you think you like before you buy, you learn a lot real fast.
Good luck