KDE 3.5 has been the best desktop environment for me (mainly due to its extreme customization facilities), far better than the contemporaneous Windows XP or Mac OS X, while the following KDE 4 was an unusable atrocious piece of garbage (despite having waited to make the transition to KDE 4 until it was claimed that all its initial bugs had been solved; when I tried it there were no bug problems, only bad design choices that could not be altered in any way).
For a few years I had kept the last KDE 3.5, but eventually I grew tired of solving compatibility problems with newer programs and I switched to XFCE.
I am still using it because I have never seen any reason to use anything else. There are a few KDE or Gnome applications that I use (for instance Okular or Kate), but I have not encountered yet any compatibility problem with them, so I have no need for one of the more bloated environment systems.
I have been using Linux on a variety of laptops and desktops, all with XFCE and without problems. XFCE does not do much, but I do not want it to do more, it allows my GUIs to be beautiful and to reach maximum speed and it has decent customization facilities, which is very important for me, as I have never encountered any desktop environment where I can be content with its default configuration.
Whenever I happen to temporarily use some Windows version for some work-related activity, I immediately feel constrained in a straitjacket by the rigidity of the desktop environment, which does not allow me to configure it in a way that would please me and would not interfere with my work.
On my main desktop, and also on my mobile workstation laptop, I have used only NVIDIA GPUs for the last 20 years and I have never encountered even the slightest problem with them, at least not with XFCE, so I am always surprised when other users mention such problems, like another poster near this message.
Perhaps my lack of problems with NVIDIA may be explained by the fact that I am using Gentoo, so I always have up-to-date NVIDIA drivers, while the users of other distributions mention having some problems with updating the drivers.
Only in my latest desktop, which was assembled this summer, I have installed an Intel Battlemage GPU, instead of an NVIDIA GPU, because the Intel GPU has increased its FP64 throughput, while the NVIDIA GPUs have decreased their FP64 throughput. Thus I hope that Intel will not abandon the GPU market, even if the intentions of their current CEO are extremely nebulous.
As an example of some very simple customizations, which are trivial on XFCE but surprisingly difficult on other desktop environments, I use a desktop with a completely blank, neutral grey background, without icons or any other visual clutter. I launch applications from a menu accessed with a right mouse click or with CTRL-ESC, and I have an auto-hiding taskbar for minimized applications and for a very small number of utilities, e.g. a clock/calendar and a clipboard manager. A few frequently used applications are bound to hot keys.