I would suggest either MarkMonitor or Corporation Service Company. They're trusted by all the biggest corporations, and handle all their domain registrations themselves.
When you're at that level of risk you probably need to worry as much about the registry as the registrar. If a corrupt registrar can simply bypass your registrar and claim the domain for example.
That's why several TLDs have a "registry lock" as well as a "registrar lock". Basically you can't transfer your domain between registrars without first going above their head to the registry.
