Qt Widgets is fantastic, but now dated since it has not been updated for the modern world. Plus it is C++, which a lot of devs dislike.
QML feels like a refresh with great ideas, bringing declarative UI and reactive programming. Where it falls short for me is it does not have feature parity with Qt Widgets, so you end up having to roll up your own components, wasting a ton of time. Dealing with layouts in QML is also an exercise in frustration.
Not having an extra language to deal with and so many features being just a flag away is why I decided to go with QtWidgets for the GUI of a project I am working on at work. And it is so nice to use despite being very old. For the graphically intensive parts I am just using Vulkan. I understand this might not be enough for all types of GUIs though and just wish QtWidgets had some sort of GPU acceleration.
QML feels like a refresh with great ideas, bringing declarative UI and reactive programming. Where it falls short for me is it does not have feature parity with Qt Widgets, so you end up having to roll up your own components, wasting a ton of time. Dealing with layouts in QML is also an exercise in frustration.