Ask:

1.    Do you really need a search engine?

2.    Do you need Boolean search capabilities?

3.    Would a specialized search service serve you best?

Once these questions have been answered, you can select the appropriate search services for your needs. If you are not sure where to begin, consider starting with a metasearch engine, like Dogpile.

And always - ALWAYS - search multiple search services. No one service covers all the Internet.