The answer depends on which method you use to determine the
coastline.
If you use the general coastline method, then Florida has the
longest coastline on the Atlantic Ocean with 580 miles. North
Carolina is second with 301 miles of general coastline. Maine is
third with 228 miles of general coastline.
If you use the tidal coastline method, then Maine has the
longest coastline on the Atlantic Ocean with 3,478 miles. North
Carolina is second with 3,375 miles of tidal coastline and Florida
is third with 3,331 miles of tidal coastline.