There are more than two types of scallops... Scallops are my single most favorite food in the world, and I probably have around 500 recipes for them. I love their sweet, delicate flavor, and their texture. They take very little time to cook. I don't like when they are prepared with tomatoes in the recipe, because imo the tomatoes overtake the flavor of the scallops. The scallops I have enjoyed in their shells are quite small... shell may be 2 to 2 1/2 inches across, and meat is small and pinkish. Scallops are very tasty served raw with just a touch of Maldon Sea salt and lime or lemon juice. Tangerine juice is good with them, too. My favorite scallops are in season only from Nvember to February, in years when the Cape waters (Cod) are not too riled up. They're known as Nantucket Cape Scallops, and they are medium sized -- maybe as big as the top joint of my thumb.
When shopping for scallops in the market, be careful NOT to get any that are sitting in whitish water. Most of those have been treated with chemicals, and the seafood will taste like soapsuds. That's not a taste I want from anything!