Both Yahoo and Answerbag are very good services, each catering to a different clientèle, and each having its unique settings. Answerbag for instance allows only a limited question length, which makes most of the questions very focused. Yahoo is a popular service with many users, and a lot of people who are devoted to the site.,
Yedda in my (admittedly biased) opinion, superceeds both, not only because of the higher level of answers, but because Yedda has a unique engine which detects people and answers, and combines the two. This way people who are interested in cars, for example, are invited specifically to answer questions about cars.
I would be interested in reading your ideas about the differences :-)
Best, and welcome to Yedda,
Neta Silberg
Yedda Content and Community Team