The easiest is probably the cruise line transportation. They will have busses, you jump on, and they take you to the airport. If there are more then one of you, it probably won't be the least expensive.

Taxis may be hard to come by, at the New York terminal sometimes the lines are huge, there just aren't enough cabs. Depends on which group you are in for departures, if you are in the first group shouldn't be a problem, if not it may be.

I would consider the car service route.