When comparing Slackware vs Linux Lite, the Slant community recommends Slackware for most people. In the question“What are the best Linux distributions for misanthropes?” Slackware is ranked 2nd while Linux Lite is ranked 34th. 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 Beginner friendly
Linux Lite renames software it comes bundled with to be more user-friendly, it gives suggestions on what additional software the user might be interested, support on how to keep the system up to date, etc. It should especially be familiar to Windows users, since the desktop layout and the basic way you interact with it is similar.
Pro Windows-alternative
It is extremely easy for a Windows user to get along with this OS.
Pro Based on XFCE
Linux Lite is based on XFCE. It makes Linux Lite extremely appropriate for old hardware without any compromise in features. Linux Lite is also loaded with lightweight apps which ensure smooth workflow.
Pro Good performance
Even on an old machine Linux Lite perform most everyday operations quickly and without stability issues.
Pro Works well with under 4 Gb RAM
Linux Lite seems to bring to life machines with 2-4 Gb RAM. There must be something that adjusts when it sees lower specs.
Pro Active forum and helpful community
The forum is pretty active and community is very friendly and helpful. The creator of Linux Lite itself is active on the forum and helps to get problem sorted out.
Pro Highly customizable
Linux Lite is a highly customizable OS. Background, icons, panel location, panel appearance, menu appearance and almost everything else you can imagine.
Pro Has an efficient Update Manager
Updating Linux Lite is made a breeze by Update Manager.
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 Working with local files can be messy
All XFCE distros are known for having little bugs here and there but Linux Lite takes the cake as local HTML files get executed as if they were shell scripts instead of being opened on Firefox.
Con Not compatible with UEFI
Linux Lite is not compatible with UEFI. You have to enable Legacy Mode to install Linux Lite. Which makes this OS a little behind latest OS.
