For oyster fanatics,the very best oysters come from the North Atlantic and are served on the half shell. Southern oysters are larger, softer in texture and better when cooked. West Coast oysters have a "cucumber" taste - that's fine, but if I want cucumber taste, I buy a cucumber.
Oysters from north of Long Island are briny and have a firm texture from the colder water. Cotuits and Wellfleets from Cape Cod are personal favorites. Sadly, most restaurants do not train their staff in how to open and serve oysters. Some restaurants open the oysters well before they are ordered, so they arrive at the table dried out. Some shuckers spill out the natural liquor, and some even rinse the oyster after opening.
Having searched for the perfect oyster bar for some three decades in all parts of the U.S., I believe that the very best is Neptune Oyster in the North End of Boston. Neptune's oysters are always fresh. There is a wide selection, and most importantly, the oysters are skillfully opened to preserve the liquor, and they are properly served on shaved ice. Excellent oysters benefit from a squeeze of lemon, but they do not need sauce. New Englanders upend the oyster directly from the shell.
Neptune oyster is not cheap, but their oysters are well worth the price if you are searching for very best. The restaurant is small, and there is normally a wait.
If you cannot get a table, you might also try one of the other excellent oyster restaurants in Boston: Legal Sea Foods, B & G, Walrus and Carpenter and the Island Creek Oyster Bar.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.