FreeBSD vs other for web hosting

[SKull]

My first priority would be security. Then longevity. Then ease of use.

So... FreeBSD?

• Security - jails - check
• Longevity - use RELEASE and don't upgrade just for the sake of it - check
• Ease of use - Unless you consider dealing with systemd and whatever firewall your chosen Linux distro uses to be 'ease of use.

The owner of said datacenter probably assumes:
"number of people using it" == "is good"