First -- it's August. Hot weather. Get a car with good Air Conditioning (I'd get a SUV for what it's worth).

The drive takes minimum four hours regardless of how you do it. But the two primary methods are coastal or Hartford. I would check the traffic on the morning of departure -- Waze is our application in the US for that information. The coastal route is prettier, but you will have a long period on a narrow motorway in eastern Connecticut. The Hartford route is wider and more high-speed but less scenic. Both routes have a natural place to stop for lunch and a bit of culture.

Coastal route:
South from Boston on the Southeast Expressway (toward Braintree), follow I(nterstate)-93 to I-95 south toward Providence. Continue through Rhode Island into Connecticut on I-95. Stop in New Haven (Yale British Museum and lunch at the Union League Club -- not a private club btw). Onward on I-95 south into NY, following the best route into Queens (usually the Bruckner to the Triborough to Queens) and cross into Manhattan at the 59th Street Bridge or the Midtown Tunnel.

Hartford route:
West from Boston on the MassPike (toward Worcester), follow I-90 to I-84 west of Worcester toward Hartford. Stop in Hartford (Wadsworth Atheneum Museum of Art and lunch at Max Downtown). Switch to I-91 south toward New Haven, but take the Wilbur Cross to the Merritt to the Hutchinson Parkway crossing into NY. Follow the Hutch to the Bronx. It also leads to the Bruckner. The rest is the same.

Both routes have tolls. The rental cars will have a toll transponder.

You can also take the train -- Acela first class is nice -- you will get two meals plus bottomless cocktails.