“Alternative DNS services, such as OpenDNS and Google Public DNS, are used to bypass the sluggishness often associated with local ISP DNS servers. However, as more websites, particularly smaller ones, use content distribution networks via embedded ads, widgets, and other assets, the effectiveness of non-ISP DNS servers may be undermined.
Why? Because CDNs rely on the location of a user’s DNS server to determine the closest server with the hosted content. Sajal Kayan published a series of test results which demonstrates the difference, and also provided the dnstest.py used so you can test which is the most effective DNS service for your own Internet connection.”