I use Google because it is by far the best out there. I ran tests several years ago using side by side comparisons between Google, MSN and Yahoo searching for the same terms in all 3 search engines. I expected minor differences but the results for MSN were startling. Any time I searched for something which was unfavorable to Microsoft or it's close business allies the results that came up on the first page of Google or Yahoo were buried 10 pages back with MSN if they appeared at all.
The whole Google China thing got me wondering who alerted the Chinese to search engine censorship. What's amazing to me is the lack of flack against Microsoft for never even putting up a fight. I strongly suspect Microsoft is who actually goosed China to start censoring search results since they have been doing it for years. Not only topics unfavorable to Microsoft, but also topics which are favorable to "enemies" and competitors. This massive bias in Microsoft search engines means I will NEVER use them for anything important.
Yahoo showed a different bias in the tests. They intermixed paid and usually very meaningless commercial hits on searches which was extremely annoying. Other than that the search results were pretty consistent with Google searches. You just had to wade through more pages of hits to get the same results.
On neutral searches all 3 engines tended to produce the same results.
Google is an Open Source bastion which contributes a great deal back to the community. Yahoo also uses open source but rarely gives back to the community. In fact you often have to work very hard to get at their protocols so that you can actually use them on something other than Windows machines. Microsoft's revamped search engine Bing is the product of a company which hates innovation, hates freedom and advocates censorship as well as invasion of privacy. Before the bad PR hit them they were big advocates of DRM for example. Even going as far as attempting to force Intel and AMD to enforce DRM at the chip level. Would you really trust something as important as your search results to a company like that?
So the choice is easy for me. Google better represents my beliefs, does the best job, is faster and I feel good about using Google. So that's what I use.