I'd say it's the most stable, but not necessarily the most lightweight, no. It certainly can be if you know what you're doing; get a netinst image and build it up from TTY and you can make it as slimline as you want. KDE is a pretty intensive suite of programs, offering almost a complete 1-to-1 replacement of Windows, so it is definitely not lightweight, but it's probaby the easiest to learn how to use Linux on, especially with Discover being an organised software store to find programs in. If you want lightweight and don't mind getting frustrated because you don't know Linux basics, don't go for KDE but try something like LXDE instead. Looks like older Windows and generally functions fine, but doesn't have Discover. You could still install it via something like Synaptic though. I believe most distros, including Debian, should have it available. You need to separate the user environment from the distro in your mind; Arch, Debian, Fedora, or other distros are just a collection of available packages which are installable and updatable via their respective package managers. Gnome, KDE, LXDE, XFCE, and other desktop environments are not bound by what distro they run on and are what you work with in the foreground. You can distrohop and use the same graphical frontend on another distro and it will work the same.