More people might be using Google search, but underdog Bing isn't afraid to challenge that preference. Microsoft's "Bing It On" challenge encourages you to do a blind comparison test to see which search engine gives you the results you prefer.
You might have seen the Bing ads about this test and the proclamations that people who took the challenge prefer Bing. While we've always known Bing was great for certain kinds of searches, the challenge is useful because it shows you the kind of searches where you might prefer Bing over Google (or vice versa).
The test does a side-by-side search of five keywords of your choice. For each round, you select which results are the best or if there's a tie.
I took the test twice. In the first test, Bing won (3 out of 5 keyword results). In the second, it was a draw. So it definitely depends on the search terms you try. For example, I preferred Bing's search results for my name to Google's, because I cared less about seeing pictures of myself (which Google results prioritises) than web pages. However, I preferred Google's results for "dogs" for the same reason — Google had more basic information results upfront compared to Bing.
Also, it's a bit hard to say this is a true blind comparison, because it's obvious which are the Google search results, thanks to Google's inclusion of photos from your Google+ circles.
Still, if you take the test as objectively as you can, you might be surprised by Bing or at least find out once and for all which search engine gives you the best results.