My answer of Philadelphia was from the viewpoint of the professional folksinger. Viewed from the jam session perspective, Dublin is terrific and so was Austin. Open bluegrass sessions are most abundant in the Richmond and D.C. areas and, back in the day, one could do a lot worse than the coffeehouses on MacDougle St. in Greenwich Village. I have never spent much time in the audience but I would imagine that NYC, with its hundreds of venues, would be a winner, as long as one didn't have to find a parking space. London, which is, at least, as populous as New York, is surprisingly inactive as an entertainment Mecca. Chicago makes London look like Camden, NJ in comparison.

                      Mike