Fortunately, there’s a tool called Namebench to test that very thing. It queries a set of nameservers and recommends the fastest configuration based on lookup speed.
I ran it and found that neither OpenDNS nor Google DNS were the fastest provider. UltraDNS beat them both by a significant margin. Though I’d never heard of UltraDNS before, I’m now using their services.
Here are some public DNS server options you can try out yourself.