My answer: Google. Why? Because it's simple, loads quickly and most of the time gives me results that are relevant to what I want. Chances are a good majority of people will also answer Google. As far as I know people use 'Google' as a verb, while other search engines, eg. Yahoo, Bing do not get the same treatment.
To be honest, I just took the use of Google for granted and never really thought much about it until I went to Ignite Sydney last week. One of the awesome talks "Everything I know about you" by Michael Kordahi tested to see if our perceptions to the search results (he comapred Bing, Google, Yahoo) would be the same if the branding was removed. The results of preference (and the search terms people looked for) are indeed very interesting - definitely worth watching!
Interesting thing was after the night I went home and gave it a go myself. For simple/basic searches (which were essentially keyword searches) all three search engines were roughly the same for me - but in picking the preferred one I actually rarely picked Google! Though for more complex searches (eg. ones which I just typed in a question) Google was the clear winner. The other two were nowhere close.
Random footnote - I hear some of you may be asking, what is Ignite Sydney? No, it is not an event where pyromaniacs go and set fire to Sydney landmarks. Ignite Sydney is a series of presentations with one very simple idea behind every presentation:
Make the presenters stick to a rigid format of 20 slides, each of which changes automatically after 15 seconds, giving a guaranteed 5 minute presentation.
This means no death by powerpoint - yay! and generally very interesting, entertaining and well thought out presentations - double yay! If you don't live in Sydney then don't worry - there are Ignite events all around the world. Have a look here for the full list