As a library vying to replace OpenSSL, the same set of suites as OpenSSL.
I'm no longer blocked on this particular issue that I filed on behalf of my work at Deno, but they aren't interested in adding less-secure suites that may be required by certain server configurations, but still appropriate for traffic that isn't general web-use.
At some point I had a list of suites required to connect to some older versions of MySQL/Microsoft SQL Server, but again, no longer blocked.
For server-to-server use where I don't control one end of the equation, I stick with the OpenSSL crate. If there's potentially older servers in the mix, I'm OK with using rustls as a backend for things like reqwest, but it'll be openssl for servers for now.
I understand the philosophy, but rustls is never going to be an OpenSSL drop-in until this approach changes.
Semi-related, I now avoid native-tls because MacOS + gatekeeper + weird JAMF configuration makes that library completely unreliable in the wild.