bring on the downvotes
Well when it comes to production systems I can tell you our uptime with HP-UX on PA-RISC (5 years been working with it with not one kernel panic) is far better than any of our Linux machines on x86_64 which are far better than uptime on Windows on x86_64 (average a few middle of night calls a year and its always Windows boxes). Haven't really ran HP-UX in production on VMs in Itaniums yet but expecting it to be worse than PA-RISC even if hardware is far faster. Intel sucks in general for uptime but Intel on Microsoft really sucks. Open and closed source both have their place. Linux can't touch the commercial UNIXs for stability in my experience though (haven't supported BSDs officially but they seem much better and closer obviously to the original UNIX code stability wise).