I trust Mozilla and the contract they have with CloudFlare (not just CloudFlare by itself) more than my ISP.

> https://support.mozilla.org/en-US/kb/firefox-dns-over-https

Mozilla has a strong Trusted Recursive Resolver (TRR) policy in place that forbids CloudFlare or any other DoH partner from collecting personal identifying information. To mitigate this risk, our partners are contractually bound to adhere to this policy.

These are much stronger guarantees than my ISP's.