When comparing Slackware vs Parabola GNU/Linux-libre, the Slant community recommends Slackware for most people. In the question“What are the best Linux distributions for desktops?” Slackware is ranked 5th while Parabola GNU/Linux-libre is ranked 15th. 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 Protects your freedom, certified free by the FSF
Pro Option to use OpenRC or Systemd
Parabola has an OpenRC edition and a Systemd edition, so users can choose which init system they want.
Pro All the benefits of Arch Linux, only 100% certified free software
Pro Very Secure
Pro Has its own repos
Parabola has its own repos (which are almost as large as Arch Linux) and the IceCat browser is included.
Pro Can be migrated from Arch Linux without a CD/USB
Pro Based on Arch Linux
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.
Con Won't work out-of-the-box on the most PC's
Almost all PCs need non-free drivers but Parabola has none to offer.
Con Same cons that apply to Arch Linux
Con Not compatible with AUR
Unlike other Arch-based distros, this free distro doesn't support AUR.
Con Small repositories
Since Parabola is a completely free distro, there is no non-free software available and the community repositories are small compared to the AUR.
Con Incompetent developers
They only care about removing "non-free" software, rather than making a properly working OS.
Con Serves no purpose
It's just Arch without non-free software and is basically a niche OS with few users.
Con Not really free
People have to pay hundreds to maintain this distro.
