There's probably valid arguments for both, depending on what kind of webservices you are communicating with, and what kind of data will be transferred.
While SOAP is a standardized protocol using HTTP to transfer XML data, RESTful web services are not a standard as much as an architectural style.
REST also uses the HTTP protocol for data transfer, but uses the HTTP verbs POST, GET, DELETE, PUT in a stricter sense. Data payloads in RESTful web services can be XML, JSON or other valid MIME types, so you're not limited to XML.
My customer now wants to communicate with an external site. I am able to choose to communicate with that service either through REST ot SOAP. Wich one should I choose?