IMO KDEs design is actually superior to anything Microsoft is offering. It is a great desktop experience, even with stock settings. Certainly better than everything Ubuntu does.
"visual design" in OSes is more of a spectrum, rather than a ranking. Windows and macOS looks better on the surface to most people who don't interact a lot with computers, but for people who spend a lot of time in front of the computer, KDE, Gnome and many other Linux desktops do a much better job to be functional, not get in your way and customizable.
Really depends on what you'd use the computer for, I don't feel like anything is much "superior" to something else, it all depends on the user and usage.
