Search engines are built by software programs. Sites are not evaluated. Most search engines only add the first 100kb of text of each web page to their database. This means text at the end of long web pages may not be retrievable. No one search engine is the best. They each have unique features.
Indexes/directories are built by humans and evaluated at least cursorily. Words searched include link and annotations, but not the full text of the web documents they point to.
Meta-Search tools are sophisticated search programs that are designed to search indexes and search engines and retrieve whatever it finds from all sources. Meta-searches are run by software. Hence resources are not evaluated.
