According to QVTKOpenGLWidget documentation, the non-native widget works only in special cases (the widget is not in a scrolling area, etc.).
QVTKOpenGLNativeWidget should work well (we use it extensively in 3D Slicer for very complex visualizations). You can try to tune anti-aliasing settings to improve appearance of lines. You may need to change the default surface format for the application if you want to use MSAA. We currently don’t use MSAA in 3D Slicer, so I cannot confirm if it works well, but there are VTK tests for that, so I assume that it does.