QtWidgets

QtWidgets is the original KDDW frontend, hence it's the most feature complete.
Although this is still the recommended frontend, you can also chose QtQuick and open a bug report for any missing feature.

By default a KDDW build will support both QtWidgets and QtQuick. If you only need QtWidgets then you should configure KDDW with:

-DKDDockWidgets_FRONTENDS="qtwidgets"

Simply to reduce binary size.

If you do have both QtWidgets and QtQuick support built, then don't forget to:

KDDockWidgets::initFrontend(KDDockWidgets::FrontendType::QtWidgets);