I'm just a regular user, not a developer or anything, so I don't know what Xamarin is. I was skeptical of UWP but I'm totally a UWP convert. It just works so wonderfully - performance is consistent, never bogs down, has all the auto updating, notifications support etc of modern app platforms etc. What I love most is how well it scales and syncs between different devices with screen sizes, pixel densities and device types. It's like magic! I still use many legacy x86 apps, but I try and use UWP wherever possible.