FreeBSD, but i would perfer OpenBSD its more secure.
FreeBSD is more secure than linux but not as secure as OpenBSD.
FreeBSD is more cryptic for a newbie.
If your not a newbie i would tell you to run OpenBSD
Theres a story a year ago for where I live that a room got sealed up and forgotten at a college here. Coulpe years later they found a 486/75 running OpenBSD in the forgotten room and there had been logons a recent as a week ago. They checked the uptime and it was 6 years.
I say BSD all the way