Define "XML processing". Each language has its own strengths and weaknesses. If you're working on an application that happens to use XML, I would put XML processing towards the bottom of the list of criteria I would use to select an appropriate language.

Personally, I am strongest in Perl, so I have a tendency of preferring it for most of my tasks. Its XML abilities have little to do with that decision.

In my opinion, Perl's XML abilities are just as strong as any other language's. For that reason, I would look at other aspects of the desired application to determine the best language for the task. Perl is good at text manipulation, so if we're talking about converting XML to/from other flexible, textual languages, I'd say that's a perfect application for Perl.