As suggested above, OP needs to provide more information about their use case and what they expect from their computer before anyone can give a meaningful response.

If you listed Linux distros on a scale from the most to the least user-friendly, say from Mint to Gentoo, Debian would come in the middle and Slackware towards the less friendly end.

Slackware is very hands-on: if you want to do anything other than run the standard installation, you need to know what you are doing. And the standard installation is not very generous with software, even though it contains the complete repository. Most users are going to need to source extra programs from Slackbuilds. Configuration usually means editing files.

Debian has the largest repository of any distro — if they haven't got it, it's probably not worth having. It's more user-friendly, but not as much as it's derivatives — in fact, providing greater ease of use is one of the goals of those derivatives.

Both are very stable and reliable. Slackware has the longer support period, if you don't mind old software and hate adapting to a new version. Debian is more regular with new versions — every 2 years — while Slackware had a 6-year gap between version 14.2 version 15. Both provide more up-to-date versions, Slackware Current and Debian Unstable — use at your own risk!

Slackware users will tell you that it sticks with tried and tested approaches and is closer to "real Unix". What they don't tell you is that many of those approaches are no longer used and no longer documented by any other distro. And what is "real Unix"? Effectively, it's Linux.

Generalisation. We're not all Apple users you know.

I'd say Slackware is ideal for the more technically minded among us. If you can't handle a CLI, then Slackware is going to be somewhat less than ideal. I'm one who always looks for the CLI... can't operate without one. In my GUIs, a shortcut to the terminal is always the first thing I set up.

https://www.slax.org/

I'm assuming both versions of Slax will have a similar look and feel on the outside, but then you'll get to experience the differences when you dive deeper into them.