I've been using both Linux and BSD since 2000. Honestly, I prefer Linux on the desktop. My dev workstation runs Arch, and I keep a FreeBSD VM running to do OS and ports builds.

As a server OS I find FreeBSD really consistent and easy to administrate. I never have trouble finding things: packages always go in /usr/local. The old-school init system works great at what it's designed to do, and all the startup scripts are easy to understand. The whole thing just feels kind of cozy and familiar. If you like working in a shell then FreeBSD just kind of feels like /home.

Coming from modern Linux though, some of the constructs can feel a bit outdated. Usually this gives me a warm fuzzy feeling, but sometimes it's a real pain (looking at you, make(1)). It's like hacking Perl, once you understand the idiom and what it's good at then you can be good friends.

If you want to run a mail server for 20 years and go through multiple hardware and OS upgrades with minimal pain and maximal uptime then you can't beat it.