Mon.itor.us, a free network monitoring site, has posted an analysis of the sites they monitor measuring server uptime and response speed. The winner in both uptime and response was NetBSD. Linux servers were 50 milliseconds faster to respond than Windows servers, and Linux’ uptime was more than 0.5% better than Windows’ (due to rebooting) — in real terms, “0.5% downtime means 50 minutes per week, or 216 minutes or 3 hours 36 minutes per month” — in every week of the survey.
Summarizing, statistically Linux based servers provide better availability and response speed than Windows servers. Absolute leader is NetBSD in both categories; OpenBSD and Solaris also demonstrate good results.