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With Silverlight's demise, I've settled on Unity 3D for cross platform games. It's a very different paradigm to Silverlight, but certainly for games it's more powerful. If you're intending on making more (i.e. new games) I'd definitely go with something like that. The HTML export is mind blowing. It's free, and there's a tonne of stuff online to get you up to speed.
If on the other hand you just want to port your old game with as little effort as possible then UWP is the obvious choice, as it's still XAML-driven. Yes, you might have to rewrite it again in a few years, but it's probably not that much effort each time.