In general, I'm happiest with a Connecticut-style lobster roll, ideally with a lightly toasted bun, melted butter, and plenty of lobster. A light dusting of Old Bay is acceptable but my no means required. (My go-to in NYC is Red Hook Lobster Pound: http://www.redhooklobster.com/)

If I'm going to have a Maine-style one, though, Luke's (http://lukeslobster.com/) makes some of the best in NYC: lightly toasted bun, not too much mayo, no celery and plenty of chilled (but not cold) lobster.