For instance, Open Text does full-text indexing, while World Wide Web Worm indexes words tagged as document titles only. Second, the design of the search engine definitely affects the comprehensiveness, precision, and relevance of returns. Often, there is a trade-off involved. WebCrawler, for example, generally returns a large number of hits for a simple keyword search, but many of them may not be relevant. Lycos may work well if precision is important, but does not allow phrase searching.
Personal preference plays a role as well.
Search forms can be simple and non-transparent, or complex but customizable. Excite offers ranked listings based on weighted comparisons of terms in documents. OpenText has a flexible search form and is fast. Output varies, as well. More sophisticated search tools produce detailed entries containing abstracts, outlines, and frequent words used.