Lobster Shacks between Swampscott and Newburyport
There is one that I was just at 2 weeks ago that was awesome- I think the name was Bobs and it was located on the road that goes into Plum Island. Coming from the bridge it's on the left- white building, picnic tables outside and HUGE portions at reasonable prices..> Great Onion Rings also...
I highly recommend- I got the combo dinner with scallops and clams for 16.99 and it was loaded with scallops and clams- also comes with fries... homemade tartar sauce was good, could have used a bit more vinegar or lemon but everything was wonderful. Both my DC loved theres- one got the combo with haddock/scallops one got the lobster roll... rave reviews.
As for the 'best', considering most come from the waters of the Atlantic, I'd say price has a lot to do with being the best. Roy Moore in Rockport has just about the best prices around, also Lobster Pool is excellent. In Gloucester, The Causeway has lobster dinners, large boiled from $18. to large baked stuffed with lobster for $27.