yahoo if your keyword has too much competition on google, or else google all the way. I get lots of traffic from yahoo on keywords that are very high competition on google and my site is no where on google for those terms but no1 on yahoo lol
Google is far better than yahoo, with the recent changes, I am finding their search results more useful and relevant.
Google is obviously better, I've never liked Yahoo for some reason. I'm just too used to Google. The user interface of Yahoo is just too bad as well, too cluttered. Even simple things like colours can help you decide which search engine is better and in my books, Google is a clear winner.
Well Yahoo does not get the number of searches that Google gets. I am on page one of yahoo (3rd result) for a particular keyword that gets 6600 searches a month in Google. Guess what? Yahoo has sent me only 3 visitors for that keyword! (since one month).
"best" is a little subjective. From the end-user's standpoint? Well, probably matters what you want. Bing, for example, seems to have a superior experience for shopping is that's what you're searching for in the first place. From an internet marketer's standpoint? Google wins for market share, but if you are ranking better on Yahoo!, maybe you like that "better".
Google is better than Yahoo as it gives more accurate results. Google takes very less time to load for any search query as well as for its home page.
It all depends on how you view them...For me it is Google. I feel more comfortable with Google search results.