I use FreeBSD and (obviously) prefer it, but:
1) ZFSonLinux has made huge steps forward and actually (at least in my opinion) is production ready and rock solid (of course it's not as good as ZFS on FreeBSD though, for example it's lacking some features and of course it's not as proven as of now)
2) Usable containers finally have come to Linux in the form of Docker and everybody is absolutely hyped about it (I would argue though that Jails has more features, is more stable and mature)
The most obvious reason for me to use FreeBSD though is just the difference in philosophy. Don't rapidly make big changes, think everything through, don't surprise users, don't make upgrades that call for massive user intervention, and it's democratically governed and yes, it's a complete OS. Code quality is also better (have you actually looked at what code makes it into the Linux Kernel?), and I would argue therefore security and stability is way better.
Just my 2 cents, nothing wrong with Linux, have used it for years, now I would not want to go back though.
And a small Side Note: No systemd, not to start a flame war, but it is taking over the linux-sphere and I find it's design just horrific