Yahoo! and MSN are competing with one another and they both have introduced (especially Yahoo!) new services to attract users.
Yahoo, the old superpower of the search engine world is now going to go head to head with the current superpower of the search engines.Google is the super search engine, Yahoo is the super directory and MSN, well, MSN is not much currently.
For the same keyword and ad copy, Yahoo seems to bring a lot more traffic faster than MSN. But in my experience MSN seems to have a little better conversion rate than Yahoo. Too bad that MSN does not have the same amount of traffic as Yahoo do.
Yahoo has more traffic than MSN because Yahoo is more famous than MSN. But in some country MSN have more famous than Yahoo. But, in world level yahoo provide more visitors.