The best type of basil for pesto is the classic Genovese basil which is a variety of sweet basil known for its large, tender, and aromatic leaves. It has a strong and distinct basil flavor with a sweet and slightly peppery note, making it the perfect choice for creating the traditional and authentic taste of pesto. However, if Genovese basil is not available, you can still make delicious pesto using other types of basil, such as Thai basil or lemon basil, which have their unique flavors that can add an interesting twist to the traditional pesto recipe.