in this post I'd like to hint you a very nice search engine: DuckDuckGo. I've been pointed out to this by a post here on why both Google and Yahoo suck (and why Google search does more).
In older posts of mine you can find some examples on how Google search can miserably fail a search.
The main problem with the two approaches is: Google (and Bing too) sorts by popularity, Yahoo by match. So, what can happen is: Google finds something completely unrelated to what you need, Yahoo is much sensible to the keywords you put.
This DuckDuckGo search engine instead, looks up the search keywords and asks you for the meaning of the words (Yahoo phase), and then sorts it by popularity (Google phase). Especially with web 2.0 and publicity, popularity of web sites loses much more importance over the actual relationship between the meaning of the search and the web page itself.
So, as usual the conclusion is: don't use only one search engine, use multiple ones because implementation matters; don't say people "Google is your friend" because it can happen to be offensive, say instead "use your favourite search engine (YFSE)".