I need to try Manjaro KDE... The only thing holding me back is WHISKER! I just love that little menu!
while my own preference is to agree with Spatry and say "XFCE" there is something to be said for KDE if you want polish and extreme ease of customization...that is the one thing I wish XFCE would do that KDE does, having the download links for themes, icons, window borders and everything else right there in UI... and it's very polished. But of course, you pay a bit of a price in weight.
In defense of XFCE, there is an option that's almost as easy. You can download and just drop the archive file into the dialogs to install them into your local user account. If you want to install them system-wide, that requires manually copying them.
But I think, in general, XFCE itself just has less polish than KDE does, and that's a direct result of it being so lightweight. KDE is more comparable to the likes of Windows 10 and macOS in terms of the eye-candy, which matters more to people than it really should IMO, but it is what it is. That being said, the fact that XFCE is being compared to KDE directly is actually a pitch FOR XFCE. I would never have put XFCE and KDE in the same category in the past. That would be like comparing LXDE and GNOME to me. They kind of serve different purposes. They're very different beasts. The fact that XFCE can hold its own against DE's like KDE and GNOME is really a testament to how good it has become. It has almost all of the features of the mainline heavyweight distros, but it uses SIGNIFICANTLY less RAM. That's impressive if you ask me.
actually vint kde plasma has been using less ram then xfce.