Norwegian/Boston - TF Green at least has MBTA service, though infrequent. 90mins to Boston. Also might pull in some trade from Connecticut by way of Providence Amtrak.
Sending it to Portsmouth NH seems way worse connectivity wise, with no Amtrak (nearest is Dover NH) or MBTA (Newburyport MA)
All things being equal, and being from Cork myself, I would rather go via SNN-BOS which knows what it's doing with international travel and isn't stuck up on a foggy hill than risk Cork to a provincial airport trying to go big time, and even more so if the road around Buttevant is fixed. Not a single international flight on TF Green's departure board today, not even to Canada which I found surprising.