Get a DeLorme atlas for each state and look for the squiggliest roads. Explore. It's always fun to discover things.
There's some nice smooth twisty bits on Route 202/9 somewhere between Rochester and Concord (NH). Can't recall exactly where. You didn't mention Maine, but I like a nice putt around Sebago Lake followed by a swim at the awesome lake beach.
Ski resort areas tend to be the prettiest rides with nice twisties. Explore a few of those. I went to a Britbike show at Sunday River a year or two ago.
Stay away from the cliche rides like 1a or the Kancamaugus Highway. The best rides are the county roads like 107 from Deerfield to Laconia, 118 from Warren to Lincoln, nearly any of the small roads in the monadnock, lakes, or Connecticut Valley regions. It all depends how far you want to ride before you get to the great roads. There are hundreds of little rides within an hour of the Mass. border. Or you can take a whole day and see how far you get.