Which is the best search engine?

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I am into research activities and usually need to search stuff on the internet. Till now I was fully convinced that 'Google' is the best search engine. 'Yahoo' came the closest second. But recently both have disappointed me so I was wondering which is the alternative best. Ask.com or Altavista? Dogpile or may be some other site. What do you think is the best serch engine? I know a few of them use the spider web technology so they claim that they scan all the pages in the World wide web but I am not sure if their claim is right. What do you suggest?