Mealy potatoes are best for deep-frying. Because they’re low in sugar, they can be fried long enough to cook them fully in the center without burning the outside. They’re also the best choice for mashed potatoes because they fall apart easily when they’re boiled.
Waxy potatoes (like these delicious fingerlings) are an excellent choice for roasting, sautéing and boiling. Their low starch content helps them maintain their shape after they’re cooked. They’re not good candidates for frying because their high moisture content makes them limp and soggy.