Unfortunately, this is not a simple question. Depending upon which meaning is used, the answer to the question varies. Although a search tool works well for one person, there is no guarantee that another person with different needs, interests and experience will reach the same conclusion about the capabilities of that tool.
Many people develop preferences for particular search tools.
After finding a search tool or two that they really like, they normally use those one or two tools exclusively. This is fairly typical behavior and will most likely happen to you at some point. The most important factors to consider when selecting a search tool is your comfort level with the tool and the ability to find the information that you are looking for. But you should keep an open mind about your preferences because the web is changing every day, and a better tool for you may arrive. To illustrate this point, take a look at the history of the Webcrawler program.