Popular DNS resolvers

Google DNS
Private and unfiltered. Most popular option.
8.8.8.8
8.8.4.4

Level 3 DNS
4.2.2.1
4.2.2.2

OpenDNS 
Old player that blocks malicious domains and offers the option to block adult content. 
208.67.222.222 
208.67.220.220
CloudFlare DNS
Private and unfiltered. New player.
1.1.1.1
1.0.0.1

Quad9 DNS
Private and security aware.
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