Welcome to LQ!
If you are indeed using Slackware currently then why the need to switch? You learn more by use of a Gnu/Linux that is not a hold your hand nor rolling. Sure the choices for Gentoo & Arch are great Gnu/Linux distro but so is Slackware.
If you stay within a 'GUI' you will learn to use the 'GUI'. Sure as admin you can use the tools that are efficient to maintain the system but if you really want to learn then learn what to do intrinsically
Depth of your understanding and knowledge will depend on how much you expose yourself to challenging task(s) or information. What level do you wish to achieve and how much time & effort for success?
Look at the beta version of 'The SlackBook
' & the new 'Slackware Doc Project
' to get some good help & information.
Just a few links to aid you to gaining some understanding;
1 Linux Documentation Project
2 Rute Tutorial & Exposition
3 Linux Command Guide
4 Bash Beginners Guide
5 Bash Reference Manual
6 Advanced Bash-Scripting Guide
7 Linux Newbie Admin Guide
9 Utimate Linux Newbie Guide
10 Linux Home Networking
11 Virtualization- Top 10
The above links and others can be found at 'Slackware-Links
'. More than just SlackwareŽ links!