Of the two, bathtub liners are the most durable option. A bathtub liner is an acrylic or PVC insert that is molded to fit precisely into your bathtub and securely adhere to the original surface.
They're durable, attractive, about half the price of replacement, and longer-lasting than refinishing a bathtub. Liners are made in a number of modern materials (acrylic, fiberglass, PVC ...