It also depends on how secret it needs to be.
For most of our secrets (those used for configuration) we use Consul.
You're putting a lot of faith in a very complex and not- well- tested codebase if you rely on Consul ACLs to protect secrets.
Of the tools listed in the OP, I feel really good about Square Keywhiz; I'm still rolling it out in my first environment, so I can't say for sure, but I appreciate the level of effort that's gone into only doing secret storage and making sure it is exhaustively tested to spec.
Thanks for your input!