I picked it for zfs. A lot of the ways things work seem cleaner and simpler than on Linux and zfs is awesome with the copy on write snapshots and filesystem compression and all that. I like rc.conf and pf is way nicer than iptables and even when you upgrade it automatically makes a snapshot so you can rollback.
Sometimes I do need to patch and compile things because people seem to not know freebsd exists but that's really the only downside.