Ranked in these QuestionsQuestion Ranking
Pro Comprehensive hardened guide in wiki
From SELinux to PaX to AppArmor to ... The wiki has got you covered.
Pro Supports custom hardened kernels
Your only real options for a widely supported hardened distro are the Red Had distros (Red Hat, CentOS, Fedora) of which Fedora is your best bet for a desktop , or Gentoo. You can make a hardened kernel in Gentoo while stripping unnecessary features, creating a much smaller attack surface, and using in-kernel mitigations others don’t.
Pro Best defense against NOP-sled malwares, even with ROP/COP mechanisms
Out of CentOS/RedHat/Fedora/OpenSUSE/Slackware/FreeBSD/Mandriva and Arch, only Gentoo can best protect you against NOP-sled malwares, even with ROP/COP mechanisms.