I'd nominate the 1987 event on the Kennebec system because those peak flows were so much greater than any others for that river's drainage.
Years 1987 cfs 2nd place (year)
Kennebec at North Sidney: 41 232,000 113,000 (1984) Relatively short POR. The 1936 peak on the Kennebec was likely between 150,000 and 180,000 cfs
Sandy at Mercer: 89 51,100 38,600 (1936)
Carabasset at North Anson 94 50,700 31,600 (2011, Irene) 30,800 in 1936
2nd place is the St. John in 2008
St. John at Fort Kent: 93 183,000 151,000 (1979)
For New England as a whole, March 1936 was probably the most widespread flood, and is the top peak flow for many drainages.