Best Shrimp in Boston and MetroWest?
Restaurant or store?
Catch restaurant in Winchester may be your best Metrowest bet. Usually nice fresh preps.
If it's really simple grilled fish, but fresh, though you'll get a lot of naysayers here, the quality assurance at Legal Seafoods remains quite strong. So if fresh is your sine qua non...
For stores, though i haven't been, New Deal in Cambridge gets lots of positives.
If you're mobile, Globe seafood shows up at many of the farmer's markets....today the Bedford FM make's its debut of the season 2:30-5, I think. Globe is usually there.