If your clients are deployed over the internet then choose message security
Jason Taylor, Prashant Bansode, Carlos Farre, Madhu Sundararajan, Steve Gregersen
Use message security when your clients are deployed over internet, as it provides end to end security.
In internet you have less control on the communication between client and service and hence every chance of having intermediaries which might break the transport security. You can use wsHttpBinding which by default uses message security and also supports interoperability
as its uses text encoding.