There are other desktop environments besides KDE and GNOME. However, they are not as widely used and supported by distributions officially. For someone coming from windows operating system in addition to KDE and GNOME, I would recommend Cinnamon. 

Cinnamon is a desktop environment made by the team that makes Linux Mint distribution. Its default layout resembles Windows, settings and default programs are easy to understand and navigate. It is easy to customize the look to the user's liking. Compared to KDE and GNOME it is more resource efficient, but it isn't as customizable as KDE. If you're willing to explore lesser used desktop environments, Cinnamon would be an excellent choice.

KDE would be familiar for someone coming from Windows. Its default layout resembles Windows. Settings and default programs are easy to understand and navigate. However, it should be noted that there are a lot of options under the hood, and it is easy to get overwhelmed. But, if you're willing to take your time and try tinkering with the options, the look and feel can be changed to the user's liking. But it can lead to an inconsistent look and feel, along with some rough edges. Comparing to Cinnamon or GNOME, KDE has the most power under the hood and can be tweaked to an extensive degree, however the default experience is very Windows like, and it would be a good choice for someone coming from Windows.

GNOME would feel less welcoming to those coming from windows operating system. However, what should be noted that GNOME is one of the most cohesive desktop environments out there. While it is less customizable than Cinnamon or KDE, it does provide a unique using experience. GNOME has well integrated virtual desktop into its workflow. There is some customizability to GNOME but, it does require a bit more work on the part of the user. However, even though by default GNOME isn't as familiar to someone coming from Windows, it does provide a unique and cohesive experience.

There are other desktop environments besides these, however for newcomers it can feel overwhelming with the amount of options. But here is a tiny list of other environments that I won't go in depth in this response. XFCE, LXQT, MATE, LXDE, Budgie and Deepin. It should be noted that none of these are bad, or wrong choices. They are niche choices, less used and supported by distributions. Between Cinnamon, KDE and GNOME, they are good options for someone coming from the Windows operating system. Cinnamon and KDE would feel most welcoming, but GNOME would provide a new and an interesting environment to explore.
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