From: http://www.dslreports.com/forum/r24566434-DNS-Best-DNS-Servers-To-Use-With-Comcast-

DNS Benchmark: https://www.grc.com/dns/benchmark.htm

GRCs DNS Benchmark performs a detailed analysis and comparison of the operational performance 
and reliability of any set of up to 200 DNS nameservers (sometimes also called resolvers) at once

From: http://code.google.com/p/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.