MAM was my first private tracker over 6 years ago and it's still my favorite community. The tracker specializes in e-learning and books. Both ebooks and audiobooks are featured. Many audiobooks are uploaded in both mp3 and m4b formats, which saves hassle of converting between the two. Fiction and non-fiction are split about 50/50. I am a non-fiction buff and I love the categories they use in audiobooks, which helps weed out a lot of the topics I am not interested in.
Thanks to the huge size of the tracker there are usually a good 100 uploads per day, sometimes more. The request section is excellent, I have had numerous very rare and hard to find audiobooks filled there with a wait time of about 10 days. Ratios are easy to maintain as free-leeches are plentiful. Usually, members shower newbies and uploaders with free points.
The best thing about this tracker however remains the sense of community. There is no rudeness (it is not tolerated). People are just generally nice and calm. Recommended for newcomers as the staff and the members take you by the hand and show you the ropes.