When comparing DarK vs Materia, the Slant community recommends Materia for most people. In the question“What are the best gtk3 themes?” Materia is ranked 6th while DarK is ranked 8th. The most important reason people chose Materia is:
Includes support for Gnome Shell, has a Cinnamon desktop theme, plus supports XFCE, Mate and all the usual suspects.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Fully supports GTK3-nocsd
The theme fully supports the GTK3-nocsd hack so GNOME3-apps will integrate well into XFCE or MATE.
Pro The color can be easily changed
A script is included to change the highlight-color to almost everything.
Pro GTK2 and GTK3
Supports both GTK2 and GTK3.
Pro Has full HiDPI support
The theme and all included sub-themes have full HiDPI support.
Pro Good support for various DEs
Includes support for Gnome Shell, has a Cinnamon desktop theme, plus supports XFCE, Mate and all the usual suspects.
Pro Under continuous active development
Responsive and helpful developer.
Pro Customizable via Oomox app
Users can build completely personal version easily using Oomox Gui app.
Pro Corresponding theme for Qt/KDE
There is a corresponding theme for the kvantum-engine under Qt/KDE.
Cons
Con Seems to not be developed anymore
Link is not working and it is not possible to find an OnyX theme for GTK3 anywhere.
Con No-GNOME etc. support
As it is made to support traditional desktop environments so there is no support for GNOME3 and its forks
Con Dark theme
It's a dark theme, so you might encounter the same issues as with all dark themes
Con No Round Corners
Let's be honest Round Corners is a must addition in 2022.