Both REST ( Representational states transfer) and SOAP is widely adopted techniques for building distributed systems. REST is an architectural style for implementing systems on top of HTTP infrastructure. A large number of Specifications has been developed on top of SOAP and there are large number of SOAP stacks both open source and proprietary out there implementing large part of this WS* stack.
Both these d techniques have their advantages and drawbacks. Here are few of the advantages and disadvantages of each paradigm.
1. Based on few simple principles which are already in wide adoption on the Web itself
2. Can be implemented very quickly.
3. Ideal for providing simple API's to the users. (Eq Whether Services, Flicker, Yahoo REST services )
4. Amount of learning required to get started is minimum in comparison to SOAP
5. Has a very large following amount the scripting community
1. If the system is a very large one, then designing based on REST could become a very complex task.
2. Implementing Security on a REST system is one major issues. Although HTTPS, and HTTP Authentication can be used, they only provide transport level security.
1. Well designed mature technology
2. Has been widely adopted in industry
3. Large number of SOAP stacks available to choose from.
4. Has support for Both Transport level and message level security which is a big advantage over REST.
5. Supports multiple protocol bindings ( Not just HTTP)
6. Ideal for implementing complex enterprise systems since the SOAP Stacks cater for security, reliability, transactions ect.
1. Complex in comparison to REST
2. Big learning curve required
3. Difficult to debug a complex system
One great thing about using WSF/PHP is that it can support Both of these techniques simultaneously. However, if you are building a complex system which require security, I would always recommend the use of SOAP.