Go ahead and use any kind of peanut butter for this Chocolate Peanut Butter Fudge recipe. Whether you use smooth or crunchy makes little difference and is left to your preference.   If you usually eat natural peanut butter and intend to use it for this fudge, make sure that you mix your peanut butter in the jar before adding it to the rest of the ingredients. Since natural nut butter doesn’t contain any added stabilizers, there tends to be a layer of oil that accumulates on the surface, and if you don’t mix it in, you could end up with runny fudge that won’t set well.    I prefer using processed peanut butter for this recipe since it blends better with the chocolate frosting.