What is the most secure FOSS operating system with Internet access?

Random people say Arch Linux, OpenBSD or Qubes, but it is true that Arch Linux is secure to an extent if it is fully hardened, but not as secure as OpenBSD, so is OpenBSD secure? Qubes is a good approach to an OS, but it's Xen security, not OS security, and I'd rather run a secure OS other than Fedora or Debian on Qubes. And I've heard that Chrome OS/Chromium OS has the highest security of any Linux OS, but it's not more secure, it's just more limited. But that, like Qubes, goes back to the drawing board. So which OS is the most secure? Maybe Multics (better protection rings than Linux, OSX or Windows)? I use the most aggressive attackers as my threat model.

I have also heard that the Windows NT kernel design, although not FOSS, is better than Linux, BSD and OSX because it is based on OpenVMS knowledge.