The Humor Research Lab at the University of Colorado, Boulder, came up with a ranking of metropolitans based on things like amounts of comedy clubs, famous past humorists, propensity of tweeting comedians, popularity in each city of comedy websites, et al... Boston, Atlanta, DC, and Portland, OR fill out the top five... it's part of the background work by the authors of a book,
The Humor Code...
NY Times article (link)
Book's website (link), with details of the study
B