Use the right tool for the job. I wouldn't say that XML or JSON is always right. But I will say that I believe XML has a better ecosystem around it; with things like XSD, XSLT, XQuery/XPath, etc., and some pretty easy to use data-binding frameworks like JAX-B. My feeling is that XML makes it a lot easier to do certain classes of things that I want to do, like taking a business event message off a queue, match it against an XQuery expression, route it to the appropriate place based on that matching, store it in an XML database where I can later locate it using XQuery, and then render it into a web-based activity stream by applying an XSLT transform.

Sure, you could get there from here with JSON as well, but it sure seems more natural using XML.