The absolute best place to go in the fall would be the Adirondak region of New York. My wife and I visited Lake Placid right at the peak of leaf season and had a fantastic time. We climbed Whiteface Mountain for an excellent view of the valley and had a wonderful experience in the many restaurants and shops around town. I would highly recommend.
I took a long weekend to Lake Placid when I lived in upstate NY and loved it. It was beautiful being able to kayak on Mirror Lake as the sun rises and I thought the downtown area was quaint. The location of the Marriott property is not ideal (a short walk from downtown rather than actually downtown) but still nice. I wish more Marriott properties were located in quaint small tourist towns.