Basically, you want to use RESTful web services for integration over the
web and big web services in enterprise application–integration scenarios
that have advanced quality-of-service (QoS) requirements.
JAX-WS: Addresses advanced QoS requirements that commonly occur in
enterprise computing. When compared to JAX-RS, JAX-WS makes it easier to
support the WS-* set of protocols, which provide standards for security
and reliability, among other things, and interoperate with other WS-*
conforming clients and servers.
JAX-RS: Makes it easier to write web applications that apply some or
all of the constraints of the REST style to induce desirable properties
in the application, such as loose coupling (evolving the server is
easier without breaking existing clients), scalability (start small and
grow), and architectural simplicity (use off-the-shelf components, such
as proxies or HTTP routers). 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.