What is the optimum time to see New England in the autumn/fall?
A lot of people do this around Columbus Day weekend (usually around October 10th or so). That’s about right for Vermont and New Hampshire, but probably a little too soon for further south. I’d really recommend Vermont. There are lovely bed-and-breakfasts you can stay at, and a drive along Route 7 is beautiful, with lots of little shops and such. It’s probably better to avoid going on Columbus Day weekend–things get really busy with the “leaf peepers” up there at that time. A week before or after would probably work just fine.