Governments are the more dangerous, objectively speaking. All of them have the monopoly of army and public forces. Not a single corporation in the world could be equally dangerous just based on this.
Are you sure? There are some pretty scary private security firms. Do you actually know what they have? I hope government really does have a monopoly on force.
No private organization has committed crimes comparable to the ones committed by authoritarian governments. I could mention USSRs pogroms, concentration camps on Germany or summary executions in Cuba, to name a few.