Meta engines do multiple queries in order to impress you and make you think they know a lot. More often than not you will do better by going directly to the search engines they use. Licensed engines are search engines that want to look like they're independent but actually are just an interface for some other engine. This category includes all such engines except for Inktomi, coz there's so many of them that they deserve their own category. Regional Engines focus on some region of the world, whether a continent, a nation, a language, or even just a state.
Special engines have an unusual format or a very specific search function.
The inclusion of an engine in one category does not necessarily exclude it from all others. And Anzwers, while also an Inktomi engine, is geared toward Australia and New Zealand. Conversely, AltaVista is best known for its engine but also has its own directory as well as partnerships with other search tools. Frankly, this categorization is a bit unfair. Each engine, no matter how much it relies on another directory, has its own unique attributes.