Secure OS

Nowadays, probably the most secure OS are hardened Linux systems (like hardened gentoo and RHEL), Trustes Solaris 11, OpenBSD, QubesOS, Novell NetWare and OpenVMS.
What do you thing is doing the best security approach of this OS.
And what do you thing is better in practise?
(You can also include other OS you consider secure)
And what do you think os security on microkernel systems?

I get the punchline: The most secure computer is one that doesn't exist.

[The more crippled and unusable your computer is, the less likely that anyone would even bother to steal it for that matter.]

 Does anyone still use computer hardware for offline, non-communicative purposes still? This is a legit question.