And what would be the number for a computer that I Turned off in November 1999, and have never turned on again? It would be zero, the best possible one. The most secure computer is one that doesn't work at all.
What we need to look for is a compromise. Something that is reasonably useful, yet reasonably secure. Different people have different weights on these factors; for some people security is incredibly important, and is worth a lot of investment of money and time. And the definition of "useful" depends on the intended use: desktop, laptop, generic server, network server, and so on. For my use case and preference, FreeBSD is an excellent server operating system; I do not use either FreeBSD or Linux on the desktop/laptop.