I used Qt Quick briefly. It seems like you get a lot of deep powerful customization, but that comes at a cost. It eventually pissed me off so I went back to QWidget, and my productivity soared.
I would not have completed my project in a reasonable time using Qt Quick. It is not "quick". Sometimes, you just want to drop tables, check boxes, buttons, etc. on to your main window, tie the click event to a slot, and call it done. You are fine with whatever default styling and rendering that Qt and the OS decide is appropriate for the widget's click/hover/etc event.
It seems with Qt Quick, you have to specify all that nonsense. Plus, the Qt Quick editor tool felt complex and confusing. I avoided it and did everything by hand. Qt Designer for QWidgets is a drag-n-drop breeze. I even got my manager on board after he saw me using it. He is an EE, and he really likes it. He is used to spending $500 on Visual Studio Pro to what Qt Designer does better for free.
Maybe I just needed to study Qt Quick more to get past the learning curve, but I knew how to do it the widget way, and I wanted the project done.
Has anybody had success migrating their project from QWidgets to Qt Quick? Unless I see a strong compelling reason, I am sticking with QWidgets. It works really well for me.