REST vs SOAP

REST

Pros

• lightweight (in all means: no server- nor client-side extensions needed, no big chunks of XML are needed to be transfered here and there)
• free choice of the data format - it's up on you to decide whether you can use plain TXT, JSON, XML, or even create you own format of data
• most of the current data formats (and even if used XML) ensures that only the really required amount of data is transfered over HTTP while with SOAP for 5 bytes of data you need 1 kB of XML junk (exaggerated, ofc, but you got the point)

Cons

• even there are tools that could generate the documentation from docblock comments there is need to write such comments in very descriptive way if one wants to achieve a good documentation as well

SOAP

Pros

• has a WSDL that could be generated from even basic docblock comments (in many languages even without them) that works well as a documentation
  • even there are tools that could work with WSDL to give an enhanced try this request interface (while I do not know about any such tool for REST)
• strict data structure

Cons

• strict data structure
• uses an XML (only!) for data transfers while each request contains a lot of junk and the response contains five times more junk of information
• the need for external libraries (for client and/or server, though nowadays there are such libraries already a native part of many languages yet people always tend to use some third-party ones)

To conclude, I do not see a big reason to prefer SOAP over REST (and JSON). Both can do the same, there is a native support for JSON encoding and decoding in almost every popular web programming language and with JSON you have more freedom and the HTTP transfers are cleansed from lot of useless information junk. If I were to build any API now I would use REST with JSON.