Well, I played around a bit and I now think, that QSplitter fits my needs better. It was just an initial desire, that all widgets, no matter their actual content, should have the same size, if possible, but it's better for the user anyway, if he has the possibility to resize the layout in some way, which I can achieve with QSplitter. I also played around with the stretch factors of my QSplitter setup and managed to get good initial sizes for that particular setup (the one with the table widget on the top left and 3 QGL Widgets).