Google just beats them all in every way. It's like the fastest, it's never down, it's got the biggest index, and it's slowly becoming more and more customisable making it even better. Couple that with the Google Toolbar with suggestions and you got the best ever search engine!! Wouldn't recommend anything else
Edit: Plus i'm willing to support a company that provides so many of the most popular services I use, for free! Maps, Google Earth, GMail and Calendar etc...