There are two species of flat (as opposed to cupped) oysters that you might be offered in North America. The first flat oyster is the Olympia oyster (Ostrea conchaphila), the oyster native to San Francisco Bay and the west coast. Olympia oysters are currently farmed only in South Puget Sound in Totten inlet and Little Skookum inlet. They are really small and grow very slowly. It takes 3 years or more to produce an oyster that is 1 to 2 inches long! Olympia oysters are also called Olys and have a sweet, metallic flavor. They accumulate minerals, giving them that distinct flavor they are so well known for. These are the oysters that were ordered by 49ers when they found gold and ordered ’hang town fry’, a plate of fresh oysters and eggs. Efforts are underway to reestablish Olympia oysters in San Francisco Bay.
The other species of flat oysters that is sometimes available is the European flat oyster (Ostrea edulis), also called the French oyster or the Belon oyster.
These oysters are native to Western Europe. They also take about 3 years to reach market size and they too have a metallic taste. Some oyster lovers consider this the best tasting oyster in the world. Due to its metallic taste, this oyster pairs well with expensive wines as the oyster will open the palate so one can better taste the nuances of the wine. I think there are many great oysters and ‘the best’ depends on many factors, not least is how they are being served and what they are served with.