[iggldiggl]

Do those return the correct CDN servers matching your geographical location and/or ISP? I didn't try Google or Cloudflare specifically, but I did experimentally used some other DNS provider for a while, until I eventually ran into the problem that by doing so I got the "wrong" set of servers for anything hosted on Akamai, where the route between my ISP and those specific Akamai servers was grossly overloaded in the evenings.

Switching back to my ISP's DNS meant getting a more suitable set of Akamai servers and reasonable download speeds again.