When comparing Slackware vs PCLinuxOS, the Slant community recommends Slackware for most people. In the question“What are the best Linux distros that don't use systemd?” Slackware is ranked 2nd while PCLinuxOS is ranked 24th. 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 Software management and updating made simple through Synaptic
Pro The team is headed by Texstar
One of the best in the business.

Pro Rolling release model
No reinstalling the OS after every major upgrade. Keep your OS updated, and you have the latest version.
Pro Helpful and knowledgeable forums
Many issues can be resolved by just searching the forums. They are really a storehouse of knowledge. If not, expert help is still available.

Pro "Batteries included" philosophy
Main release includes most apps needed by users everyday. Windows users will see a familiar look and feel to the UI. H/W issues practically nonexistent, as most drivers come with the ISO.
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 No 32-bit version

Con Gaming can be hit or miss
To run some titles, particularly from Steam, some "massaging" is necessary.
