For Spaghetti alle Vongole, it's traditional to use small to medium-sized clams with thin shells such as Vongole veraci, manila clams, or littleneck clams. These clams have a sweet and delicate flavor that pairs well with the recipe's garlic, olive oil, white wine, and parsley. It's important to use fresh clams that are still alive, so make sure to buy them from a reputable source and check that they are tightly closed or close when tapped. Discard any clams that remain open or do not close when tapped, as they may be dead and unsafe to eat. Also, rinse the clams thoroughly under cold running water to remove any sand or grit before cooking.