The speed of your DNS service usually depends upon the location of your website viewers. If your service provider has a server close to your audience's place, it will load your web pages much faster than usual.  You should always select a DNS server that has data centers distributed all over the world. It will help in loading your website faster, despite the user's location. However, if you target the audience from a specific country like the United States, you should choose a DNS service with the most servers in the country.