Most Linux distributions I've played with (CentOS, Redhat, Ubuntu Server, Debian) are pretty mediocre when it comes to security. I've actually stopped using Debian since this incident :
http://www.debian.org/security/2008/dsa-1571
In addition, my own experience would point out that OpenBSD is more reliable than Linux, but I'm just a single data point.
For development however, we use FreeBSD for a wide range of reasons including ports freshness.