For pure clarity, a glass or mineral glass lens is the best. But most people prefer polycarbonate lenses, which are lighter and more durable. High-index lenses are good for those who have strong prescriptions that would normally require thicker lenses. These high-tech plastic lenses end up being the same thinness as standard plastic or polycarbonate lenses that have a lighter prescription. However, you do have to pay more for high-index lenses. Arguably the best lenses are Trivex lenses, which are lightweight and durable and offer slightly better clarity than polycarbonate lenses. But they are more expensive than plastic (CR-39) and polycarbonate lenses.