From the perspective of a Windows user, GTK+ 3 does a less-good job of fitting in than Qt Widgets 5. Even with the win32 theme (GTK seems to use the Adwaita theme by default) GTK is missing shadows and the icon gutter in menus, and animations on push buttons and scrollbars. Qt Widgets 5 (with the Windows style, not the Fusion style) gets those right, and as a result, Qt apps look much more like native apps.