The fastest route from New York City, in our experience, is to take the Hutcheson to the Merrit to the Wilbur Cross (both CT 15) to I-91 north.

The next fastest is to take I-684 to I-84 to Hartford, then I-91 north.

The most scenic is to take the Taconic to NY 295, just before the end, take that over to NY 22, take that up to NY 7 and go east (right) so on it, which will become Vermont 9, which you can take across to I-91's Exit 2 at Brattleboro. Go north on I-91 then, either to Exit 3 for the ceremony, or Exit 5 for the rehearsal. Expect this to take an extra hour -- roughly five instead of four.

A just-slightly-slower and definitely more scenic variant on that scenic route, if you're coming to the rehearsal (wouldn't make much sense for the ceremony) is to take Vermont 100 north from Vermont 9 at Wilmington, Vermont, then take Vermont 30 "south" (mostly east) from East Jamaica to Townshend, where you'll turn left onto Vermont 35 north. Take that until it ends at Vermont 121, where you should turn right and go east to Bellows Falls. As you're entering Bellows Falls, take either the sharp left onto Pleasant Street, or either of the next two lefts onto West or Center, and follow the local directions elsewhere here.