It really depends on the types of people you wish to attract. Obviously this is very subjective but I've always found mailing list discussions to be of noticeab

It really depends on the types of people you wish to attract. Obviously this is very subjective but I've always found mailing list discussions to be of noticeably higher quality than forum discussions. If your topic is a technical one then a mailing list makes sense, whereas a support area for average Joe really wants to be a forum (actually, Facebook groups seem to have taken over a lot of the area previously carved out by forums, and the standard of discourse is lower again).