I have not tried Xamarin. Qt works well on iOS and Android. This does not give an accurate internal look and feel, and the transition to many different resolutions and screen sizes becomes painful. I recently finished publishing a Qt application using Widgets, QML, iOS and Android (and Mac and PC).
IOS pop-up support is weird. Style sheets are very useful. Controlling the pop-up keyboard and the Finish button is a bit weird.
Overall, it's still Qt, and it's a terrific cross-platform tool. Signals and slots are great.
Hope this helps.