The most popular sour variety of which fruit is the Montmorency used in pies?

According to National Public Radio (NPR), the most popular pies bought in the store are Apple, pumpkin, cherry, blueberry, and Dutch Apple. However, their survey found that Apple pie is the most popular, with strawberry-rhubarb second most popular, then pumpkin, cherry, and blueberry.

According to USA Today, Apple is the most popular pie followed by pumpkin, strawberry, cherry, and blueberry.