I would have to say, if my life depended on the OS staying up without fail, to the degree of 99.99999% of the time, I'd go with the following:

Slackware: similar to gore, can't get it to actually crash.

As far as corporate OS', there's only one real answer I think I'd go with.

Solaris 10: with zones and containers and the 128-bit zfs filesystem (no, the z no longer stands for zettabyte, per Sun at the bootcamp I was at), virtualization is at a whole new level not to mention in cooperation with SPARC hardware, the 4 threads per core makes for great performance.

What I wouldn't run it on:

Redhat anything...
Microsoft anything...
Gentoo...dumbed down linux IMHO.
Mandrake...RH clone IMHO.