One can't argue with Netcraft. Ok, one can (for starters, uptime alone is an unscientific indicator of OS stability), but FreeBSD's rock-solid stability and reliability are nonetheless legendary and widely documented. FreeBSD is the OS behind many of the world's most high traffic websites.
If you prefer your evidence colloquial, the machine below has been operating as a dedicated, publicly-accessible OpenVPN server for one of Jimbo's customers for nearly three continuous years with no downtime. (Only the fact that it's a laptop has allowed it to rack up such a big uptime - the power company's not nearly as reliable as the OS!)