When comparing Slackware vs openSUSE Tumbleweed, the Slant community recommends Slackware for most people. In the question“What are the best Linux distributions for desktops?” Slackware is ranked 5th while openSUSE Tumbleweed is ranked 60th. 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 Stable
Tumbleweed is stable enough to use every day. Updates are OpenQA tested to ensure stability before being released for Tumbleweed. Bleeding edge untested software can be tried using OpenSUSE factory.
Pro Easy installation and cutting edge apps
Pro A large amount of software
Pro Tumbleweed + OpenSUSE Build Service
Pro Good selection of preinstalled applications
Pro User friendly + Good support
Active and friendly user community, updates come fast
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 Little / no third-party support
Like it or not, most third parties don't want to deal with less-popular distros. So most of them only support Ubuntu LTS and those versions of RHEL/CentOS that are still supported.
Con Complex multimedia codecs and plugins installation
Con "Online Update" update in YaST control center only works in openSUSE Leap
Con Packman repository has to be added to have good software support
Con Slow and painful unfortunately, especially compared to other modern distros
