In the past, yahoo has always indexed more pages and given nearly double the results of its competing search engine and all of our favorite, Google. Yahoo still gives a lot more results than Google and for the reason that Yahoo is less lazy. They send out a lot more yahoo slurp bots than google and I notice that from looking at my forum. Nearly 300 times more yahoo bots than google bots visit my forum everyday.
Yahoo also returns more search results because of those bots. They go around and index more pages based on the site content. If you want more results yahoo is probably the way to go but sometimes google narrows down your search greatly. But again if you like bigger numbers, maybe yahoo is your best bet.