I’d pick the one that supports IPv6 and then make two separate requests to it. One request over IPv4 and one over IPv6.
curl -4 https://www.cloudflare.com/cdn-cgi/trace
curl -6 https://www.cloudflare.com/cdn-cgi/trace
Also the reason that the 1.1.1.1 one shows only IPv4 address is because 1.1.1.1 is itself an IPv4 address. So any connection to it will have to be using IPv4.