ArcGIS viewer for Flex vs. Silverlight vs. Using HTML 5 for ArcGIS

Both ArcGIS viewer for Flex and Silverlight are both applications that make it possible for users to create their own web GIS applications and make them available for intranet and Internet use by using a web serve. The viewer for flex is produced by Adobe and has been around longer than the viewer for Silverlight which is produced by Microsoft; thus, there may be more valuable resource available for flex viewer than for Silverlight viewer (widgets for flex viewer, add-ins for Silverlight). Flex web applications can be developed by using any IDE that supports adobe flex (i.e., Eclipse and Adobe Flash Builder). Silverlight applications can be developed with any .NET programming language (C#, etc.); or software can be used in the form of Microsoft Visual Studio.
Developing a Flex viewer widget, however, appears to be much easier than developing an add-in for Silverlight viewer. To develop a Flex widget, you use ArcGIS API for Flex (using the same framework for extending the viewer and developing your own applications from scratch). With the Silverlight viewer, you need to use a separate application, ArcGIS Extensibility SDK for Silverlight, which looks a bit more complex to me compared to ArcGIS API for Silverlight because it follows the Model View ViewModel (MVVM) pattern. With the Silverlight viewer, appears to let end users modify symbology of layers in the created web applications without modifying the original application configuration stored on the web server. I can see this being useful if you don’t want to publish multiple services with different symbology tailored for different users, but instead want let your users specify how layers should look in this particular application session (i.e., printing a web map to a .pdf file with the custom symbology, etc). This may be able to be done in ArcGIS viewer for Flex but I have not been able to discover how; it could be possible with a custom widget but I am not sure. Another note of functionality that I’ve noticed is that ArcGIS Viewer for Flex can be downloaded with its source code available, while ArcGIS Viewer for Silverlight does not come with the source code, giving more options for Flex viewer customization via programming.
However, advances in modern browser technology combined with limited browser support for Flex and Silverlight, have begun the encouraged use of JavaScript/HTML5 for web GIS applications. JavaScript/HTML5 seems to have become the technology of choice among our user community for web GIS. Given this shift in technology, Esri will encourage the use of the ArcGIS API for JavaScript to build custom and out of the box web applications. They have been advancing JavaScript API to integrate new ArcGIS platform capabilities such as 3D visualization, enhanced vector rendering, and stream layers. Capabilities that will not be added to the Flex and Silverlight APIs.