When comparing Slackware vs Solus, the Slant community recommends Solus for most people. In the question“What are the best Linux distributions for desktops?” Solus is ranked 11th while Slackware is ranked 32nd.
Ranked in these QuestionsQuestion Ranking
Uses stable, plain-vanilla packages from upstream.
Pro Ideal to learn more of Linux
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 Most oldest linux distro
Slackware project was started in 1992. It is only one of the old distros which is still active.
Pro Rolling release
Pro Modern desktop environment
The default desktop environment used by Solus is called Budgie and is quite nice and minimalistic.
Pro Easy installation
The installation procedure for this distribution is quite simple. It's GUI based and all you have to do is to follow the instructions given by the installation window itself.
Pro Great package management
The software center makes it really easy to install the latest software through Snappy and Flatpak. Including third party software.
Pro Exclusively for desktop systems
System boots quickly and stays responsive. Does what operating system should do, and does it really well.
The system itself is very stable. All packages in the repository seem to be carefully picked, well prepared and run stable.
Pro Seamless Packages
It may not have the most obscure packages, but the packages it does have is a good number of everything a Linux user needs. Gamers, developers, desktop users, etc. all have the necessary packages and then some. The packages themselves are integrated perfectly and are very well updated.
Pro Built from scratch
Con Large size live ISO
One need to vain 3GB+ data for downloading one slackware ISO.
Con Slow development
Con Software a bit slower to launch than for other distributions
Con Forums are not very friendly
Con There is often a black screen after update
Con An upgrade breaks the system quite often
Con No USB Image writer
Con The default desktop environment is not very customizable
Maybe because it's a relatively new project still in its infancy and this may be fixed in the future, but Budgie is not very customizable. You can only change the theme and wallpaper.