I have an older model Dell laptop running WindowsXP that I would like to transition to Linux in order to lrarn the system. I think the KDE version would be the most "friendly" for me as a rank beginner.
Should I start with KDE, or would Ubuntu or Mint be better?
Answer to the question
KDE is a fun desktop gui interface to use on Linux. It is very customizable and just looks pretty. It can go wonders if you know how to use it.
Yet, in my opinion, it can be a too much to learn for a beginner who is just starting out with Linux. The learning should be smooth, easy to grasps the concepts. You don't want to overwhelm yourself on your first try. I would use KDE when when you become more advanced with configuring your desktop gui interface.
For starters, navigate Linux using something more relaxed like XFCE, LXDE or Mate. These desktop environments are low-key meaning, they make it easy to get around your system, you understand how things are organized from a gui perspective. XFCE, LXDE and Mate feel more window XP like. The layout will look similar. Customization is very easy. You are on the right track if you decide to use a Ubuntu-based distro. That system was made to make using linux easy for everyone.
Once you get comfortable using Linux then you can try something more advanced like, Unity, Gnome or KDE, or perhaps, slackware, ArchLinux, Fedora, CentOS etc.
First tread slow and smoothly, then kick it into high gear.