It’s common practice to use the DNS provided by whoever your ISP is to resolve names on the Internet, but in some cases the ISP’s fail optimize or maintain their DNS server(allocate resources) resulting in poor performance.
Fortunately, a large number of alternative public DNS providers exists, the question is ‘Which one do I use ?‘. The answer to this question can be provided by Namebench a free and open source DNS benchmarking tool.
Namebech does not measure long term reliability.
Description from the Namebech home page
Try out namebench. It hunts down the fastest DNS servers available for your computer to use. namebench runs a fair and thorough benchmark using your web browser history, tcpdump output, or standardized datasets in order to provide an individualized recommendation. namebench is completely free and does not modify your system in any way. This project began as a 20% project at Google.
The whole DNS benchmarking test will be done for you automatically, actually all the user has to do is Download > Extract > Run Namebench and click on Start Benchmark . Wait four to five minutes for the test to be completed, when done Namebench will present you with the results by opening a window on your browser.
Hopefully, the results will help you make an informed decision on whether you should change DNS provider at all.
Namebench Home Page http://code.google.com/p/namebench/