I was always told by colleagues 184.108.40.206 appears to work faster and have to combine that with Google's public DNS. Basically using 220.127.116.11 as primary and 18.104.22.168 as secondary. However, Google only provides 22.214.171.124 and 126.96.36.199, so who provides 188.8.131.52? And if true, why is 184.108.40.206 faster?
Note: These IP addresses are used to dig domains and to determine if local DNS changes has propagated over all over the internet.