I use Google DNS because I feel it suits my personal theory of privacy threats. Among the various public DNS resolver services, I feel that they have the best technical defenses agains insider snooping and outside hackers infiltrating their systems, and I am unperturbed about their permanent logs. I also don't care about Quad9's logs, except to the extent that it seems inconsistent with the privacy story they are selling. I used Quad9 as my resolver of last resort in my config. I doubt any queries actually go there in practice.