If you plan on keeping the walls aroung the tub, refinishing the tub is a way to go and there are several methods (spraying the tub or liners over the tub). If you are redoing the walls around the tub this usually exposes the wall studs then replacing the tub makes more sense. You get a better and more durable finish from the factory on a new product than one that is applied in your home. It is a little more expensive but definately?worth the money.