Currently, it's #key-1. Less is better. Also, #0 looks less like something that's supposed to be filled in. See https://github.com/quartzjer/did-jwk/blob/main/spec.md for an example in the wild.

Note that using fixed key ids does not prevent DID resolution caching since the cache would not be hit when any of the DID resolution options differ, in this case x509chain.