It really depends on what your use cases are for the ESB. Asking on either forum would give you biased results. Its probably better to do an evaluation based on your own needs.
The book Open Source ESBs in Action (http://www.manning.com/rademakers/) has a section that compares a number of ESBs, including Mule and JBoss ESB. The ESB comparison section is probably worth the cost of the book (some companies pay thousands of dollars for similar studies).
What is your rating for Mule and Jboss out of 5 for the following services.
5.Character code conversion.