Safety and security are defined differently around the world. If I were to rank secure sites if the meet, for example, Mozilla privacy and security standards (https://foundation.mozilla.org/en/privacynotincluded/about/methodology/).
Ideally, I would like to see that they have security certifications (ISO27001, SOC2 Type 2, etc) a bug bounty programme or some sort of third-party verification (pentesting, daily vulnerability scans, etc.)
There are many criteria that can be applied, so if you don't want to do the checks yourself (or have an advisor to do it), perhaps you can rely on certifications if they're available.
