At first glance, HTML5 and Silverlight are similar in a number of ways. The similarities are tied to ease of deployment and the richness of the user interface. In terms of their interaction models, neither demands that one wait for a page refresh, and working with either is similar to the way one works with a desktop application.
Functional similarities between HTML5 and Silverlight tend to dissolve on closer examination. Silverlight is more suited for intranet applications that have relative control over the deployment environment than for true Web-based deployment. If you look a little deeper at the deployment scenario in Silverlight, it is still not a true end-user solution. If the developer’s purpose is to have application users download Silverlight and run it on their machines, then the developer needs to have a good picture of the customer.
In cases of an intranet solution where developers have more control over the machines and know that they are Windows machines, they may not have quite the degree of control needed for a desktop application, but they know that those machines are capable of running Silverlight, providing the developer with a great deal of flexibility.
Silverlight is limited if mobile deployment is required. Currently, Silverlight is only supported on Windows Phone. It may be supported on other platforms in the future, but this is not certain. If developers don’t have control over their mobile clients yet they want to support them, HTML5 is a viable option. Already supported by iOS, Android 3, and with Windows Phone committing to support it in IE10, HTML5 is the clear choice right now.
Silverlight and HTML5 both have a place and a purpose. Today, if you expect to run on desktop, Web browser, and Linux, the only choice is HTML5. If you’re not looking for a wide deployment and have short-term goals, Silverlight is the way to go since a lot can be carried over to the HTML5 environment. As long as developers make an informed choice, either Silverlight or HTML5 is fine.
For more information, read more about the debate between HTML5 and Silverlight at InfoQ.