(part-time resident...)
Define "seafood" and what would count as "best" for you. Not being snarky. There's just such a range of what could be meant. Shrimp tacos? Grouper filet? Ceviche? and so on.
Note that while some days I REALLY want a shrimp taco at El Camaron Dorado. However, shrimping isn't really done locally, so that shrimp, though great, isn't going to be nearly as fresh as in, say, Galveston. "Fresh" will actually limit some responses.
People are going to name La Perlita for lionfish, La Conchita del Caribe for whole fried fish that you select from a cooler, and Pescaderia San Carlos for fried grouper filet. Those would all be great answers.