Which DNS Server You Should Use On Your Computer?
The job of a DNS server is to translate domain names (like google.com) into IP addresses (like 126.96.36.199) and it does this for every new new site that you visit in the browser. Therefore, no matter how fast your Internet connection speed is, a site won't load unless the DNS server has performed the lookup successfully.
When it comes to choosing a DNS server, you've several choices. There are public DNS services like OpenDNS and Google DNS or you could use the DNS Server of your ISP itself. To find your current DNS server, type 'ipconfig /all' at the command prompt and look for the "DNS Server" entry under Ethernet adapter.
The speed at which a DNS server can resolve domain names into IP addresses depends on its geographic location among other factors. Therefore, for example, OpenDNS could be the fastest performing DNS server for a user in location A but Google DNS could be a better choice for another user in location B. This also explains why your ISP's DNS Server may perform faster in some cases.
If you would like to know which is the fastest DNS Server for your computer, there's a free utility called DNS Benchmark that can help. It will test the speed of all the popular DNS Services, including OpenDNS and Google DNS, from your computer and then arranges them in the decreasing order of performance.
The bars represent the average time it takes for a DNS service to resolve web domain names into their equivalent IP addresses and thus, the lower the better. DNS Benchmark is Windows-only but Namebench is a good option if you are on Linux or Mac. For some reason, I could not get Namebench to work on Windows 7.
Most DNS services offer resolvers at two IP address - for instance, Google DNS is available at 188.8.131.52 and 184.108.40.206 - and they are used in the same order in which they are listed in your network settings.
You should therefore look at the performance of individual DNS servers and set the "Preferred DNS Server" as the one that has the lowest score. In fact, you may also mix servers - like you can use Google Public DNS as the Preferred DNS server and OpenDNS as your Alternate DNS server.