The Java EE 6 Tutorial, Volume I

When Should I Use JAX-RS?

When compared with JAX-WS, JAX-RS makes it easier to write applications for the web that apply some or all of the constraints of the REST style to induce desirable properties in the application like loose coupling (evolving the server is easier without breaking existing clients), scalability (start small and grow), and architectural simplicity (use off-the-shelf components like proxies, HTTP routers, or others). You would choose to use JAX-RS for your web application because it is easier for many types of clients to consume RESTful web services while enabling the server side to evolve and scale. Clients can choose to consume some or all aspects of the service and mash it up with other web-based services.