When comparing Slackware vs Red Hat Enterprise Linux, the Slant community recommends Slackware for most people. In the question“What are the best Linux distributions for misanthropes?” Slackware is ranked 2nd while Red Hat Enterprise Linux is ranked 115th. The most important reason people chose Slackware is:
Uses stable, plain-vanilla packages from upstream.
Specs
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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 Each version is supported for a really long time
Each released version of RHEL is supported for around ten years by Red Hat with constant bug fixes and security updates.
Pro Greatly favours stability over anything else
RHEL favours stability over being up-to date. For this reason it ships with packages that may be up to two years behind in order to ensure stability over everything else.
Using older versions for packages means that they have been thoroughly tested and used in production for quite some time, and are ensured to play well with each-other.
This strategy has paid off quite a lot in the past. One example is the Heartbleed bug which left RHEL unaffected since it was using a two-year old OpenSSL library which did not have the bug.
Pro Rapid security updates
Pro Built-in disaster recovery solutions through clusters
RHEL has several built-in solutions for disaster recovery. For example, it comes with pacemaker which can be configured to manage multi-site and and stretch clusters across multiple geographical locations for disaster recovery and scalability. It can also be configured to trigger notifications when the status of a managed cluster changes by using enhanced pacemaker alerts.
Pro Applications don't have to take into account potentially breaking changes in libraries
Since RHEL backports all updates and bug fixes to older versions in order to maintain package compatibility across releases, applications hosted on Red Hat Linux don't have to worry about potential breaking changes in libraries they use, especially language libraries.
Pro Best support as far as hardware goes
This distro is by far the one with the largest number of certified server-class hardware.
Pro Built-in support for containers
Comes with built-in management tools for containers (Atomic CLI, Cockpit) and a container runtime in the form of Docker engine.
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 You need to buy a license
RHEL is a commercial Linux distributions and it's rather expensive as well, the cheapest license costs $349.
