When comparing Slackware vs Hardened Gentoo, the Slant community recommends Slackware for most people. In the question“What are the best Linux distributions for misanthropes?” Slackware is ranked 2nd while Hardened Gentoo is ranked 36th. The most important reason people chose Slackware is:
Uses stable, plain-vanilla packages from upstream.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Stable
Uses stable, plain-vanilla packages from upstream.
Pro Strong adherence to UNIX Principals
Pro Ideal to learn more of Linux
Follows the original Linux roots. It still sees Linux as a free clone of UNIX so the distribution tries to be UNIX-like.

Pro Package management
Uses standard tar archives with shell scripting as packages.
Pro One more distro which is init based
Some users don't like to install systemd based distros because they increase booting and processing speed.
Pro Oldest surviving Linux distro
Besides Debian (which was first released in August 1993), it is the oldest still maintained Linux Distribution and was first released in July 1993.
Pro Super fast
Pro No systemd
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 Comprehensive hardened guide in wiki
From SELinux to PaX to AppArmor to.... The wiki has got you covered.
Pro Fully customized kernel that prevents server-side malwares with SSO mechanisms
Out of CentOS /RedHat/Fedora a hardened kernel is very easy to make.
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.
Cons
Con Not user-friendly
It is made to be KISS (keep it simple, stupid), so you have to do everything by hand.
Con Large size live ISO
One needs to vain 3GB+ data for downloading one slackware ISO.
Con Narrow repos
Doesn't offer the same amount of options as other distros do.
Con Niche/small community
Slackware is its own niche and has a small community.
Con Very slow release cycle
Hasn't updated in 3+ years.
Con Dependency issues
When it comes to dependencies, Slackware shows more issues than many other distros.
