The automation of Web services interoperation can bring advantages to effective B2B collaboration. However, the techniques for Web service composition may still require a lot of manual efforts. For example, how to select the most appropriate service for service composition is far from trivial. This paper proposes a method for best selection which can perform the most appropriate selection in composition process. Given a selection policy such as minimum cost, the method can find the most appropriate service. Experiments show that the method proposed sometimes only takes a little more time than that without selection policy to select the best composition plan.