What exactly are the differences in these? Can they not all be made to look "like each other," even though each one is able to be customized?
I noticed that each had their own look about them (for example, Xfce with the thin toolbar at the top), but then I started noticing people showing off their desktops online with different DEs looking like other DEs (what traditionally looked like Xfce was made with KDE, etc.)
So, what are the main differences? I'm mainly interested in the differences in appearance, since apparently they can all be made to look alike.
Side question: Please rank them from most lightweight, fast, and stable to least lightweight, fast, and stable.
actually is a lot of difference between desktop environment
the main difference between them is how they interact to user throught they own 'look and feel'
Yes, they can be made to look almost like each other, but you can also make them completely different each other. althought how to costumized them is different from each other.
You can try them one by one by using VirtualBox or Vmware
Lightweight and fast? LXDE or BlackBox
Solid and Stable? i think KDE is most stable, but Gnome is not bad either.... but both of them eat your resource a lot tho
User Friendlines? Cinnamon, Pantheon... these two is the best user interface for new user
least stable, etc? idk dude, its depend on your setting and all... i think now days GUI is getting better and eat less resource tho
i personally use KDE Plasma 5 (Kubuntu 18.10) as my Desktop Environment. You can try every Desktop Environment as choose what suit you the best.