Certificate-based SSH authentication is superior to SSH keys in many ways:

• SSH certificates intrinsically possess a validity period before and after which they are invalid for providing authentication.
• SSH certificates can be embedded with SSH restrictions that limit:
  • Who can use the certificate
  • The list of available SSH features (X11Forwarding, AgentForwarding, etc)
  • Which SSH client machines can use the certificate
  • Commands that can be run via SSH