My favorite kind is whatever seems to be working at the moment!
With my latest release, FOR KICKS, I scored an interview in my local paper. Will that help? I hope so...plus it was fun
I like guest blogging -- it is fun and as long as you are careful where you blog, has its own built in audience.
Yahoo Groups have never had much impact for me...I always wind up on the loops with the people asking when the giveaway is, and never see a rise in sales. The same thing with internet chats. I wish they were more productive for me.
Giving writing workshops to local writing groups seems to help with print sales, but not as much with ebook. I bring postcards or bookmarks with my book info. One group actually hosts a booksigning as part of the meeting.