I point dnsmasq on my home router at Cloudflare DNS and then add two exceptions:

  server=/att.com/68.94.156.11
  server=/att.net/68.94.156.11

(These used to be needed for their account portal to work properly but I don't know if that's still true.)

I also used to point my streaming devices at AT&T's DNS servers in order for CDNs to properly serve from the closest location, but that no longer seems necessary, so I guess the CDNs have gotten smarter (anycast maybe?) since Cloudflare doesn't send EDNS Client Subnet information in its queries.