Are you traveling from Boston to New London, CT, then taking the ferry to Orient Point and renting a car? Are you doing this by train to New London? Or renting a car in Boston?
For "best way" are you interested in the least expensive way? Or the most expedient way? The most expedient would probably be to rent a car in Boston, put it on the Long Island Ferry, use it at Sag Harbor, then drive to a NYC rental car drop off location.
It's hard to predict what that one way car rental would cost. It varies. Sometimes there is a huge fee for the one way trip and sometimes not. Use Kayak.com or similar sites to price compare.
You mention "we". If it's a family, the cost of train tickets from Boston to New London, and from LI into the city could add up. Take that into account as you price compare.
Sorry...I should clarify. We (party of 4) are thinking we should take the train from Boston to New London, rent the car, put it on the ferry to Orient Point and then keeping for the days in Sag Harbor and returning it at a nearby drop off before heading into the city via train. Everybody is nervous about driving it into the city. I don't want to be moving at a snails pace, but don't mind sight seeing & would like it to stay somewhat economical.
Thanks for the help!
IIRC, the ferry terminal in New London is a short walk from the train station. So one option would be to take the ferry but wait until you got to the Long Island side before you rented a car. There don't seem to be any car rental places right at the ferry terminal, but there is a Hertz and an Enterprise not that far away.
Since Enterprise always advertises that it will "pick you up," you can see if they would do that from the ferry. A Hertz "local" office might do the same.
I'd price out all of these options.
Coming from the North Fork you can either take the ferry to Shelter Island and then from Shelter Island to Sag Harbor, or just drive around via Riverhead. I've always preferred the Shelter Island route, but either would work.Edited: 05 August 2014, 10:08
I would recommend the Hampton Jitney, leaves from center of Sag and runs to the city. There are multiple buses each day and make stops in mid town and uptown. To take the train you will have to drive to either Bridgehampton or East Hampton park and then get the train.