Free Silverlight 5: HTML 5, a comparison
The blog Eternal Coding does an excellent job of comparing Silverlight 5 versus HTML 5. Of course the boils down to XAML versus HTML 5.
It is a great read, you might want to print it out and take it to the beach (I still can’t bring myself to taking personal electronics to the beach).
https://blogs.msdn.com/b/eternalcoding/archive/2011/06/13/html-5-vs-silverlight-5.aspx