The choice between
SOAP WS and RESTful WS depends on how strongly you want the contract between the consumer and producer to defined.
If your WS is intented for B2B exchanges and can be used potentially by other external companies I would go for SOAP which strongly
defined the contract via WSDL.
If your WS is intented for internal use only in your company and the interface is simple enough like in your case, there is no
need for the SOAP overhead and I would go for RESTful WS.
I discarded here the social type of B2B integration where for example the MSN website calls the Facebook RESTful API to display
you facebook status in MSN. That's a particular case.