Also, unless you have a very good reason for doing otherwise, please include a JSON version of your API. JSON libraries are just about ubiquitous and it causes far, far less pain than SOAP.
Except for consuming the API directly in a browser, there's little reason that XML should cause you pain.
I disagree. Unless the data I'm working with are awkward/difficult to represent in JSON (ie, they're highly structured documents, for which XML is ideal), XML is always more painful to work with. More painful to produce and to consume.
This is working primarily with Python and Javascript.
XML in iOS is a beast, and a real pain to read (and I've never attempted to write it).
Plus, on mobile devices especially, XML is slower to download because it is more verbose than the equivalent JSON object.
So I agree, unless you need a highly structured document, I always go with JSON over XML.