I think the real-world experiment that I like to call The Internet has largely answered this question. Goole commands over 60% of the US search market and its share is still growing:

comScore April 2008 U.S. Search Engine Rankings:

Google 61.6%

Yahoo! 20.4%

Microsoft 9.1%

AOL 4.6%

Ask 4.3%

They all suck because like you have to always change your preferences if you want to look at porn. . .

Google, for the reasons stated above. Also, the various other Google products (Notebook, Gmail, etc) tie in well with Google search, and Google makes it easy to implement their search in other websites.

Google always has the most relevant and up to date results of any search engine, thus I think they are the most superior.

Clusty, because not only does it query major search engines for results, but it also displays results in a clustered form; in other words, you can easily narrow your search down. I use it heavily while scouring the web for evidence to use in team policy debates.

Google. Although, Yahoo is pretty good.

I would say Scour, because you can vote and comment and get points. It is more fun than an ordinary search engine.

http://scour.com/invite/codler