Which interface for a modern application?

HTML 5 , QML, XAML, platforms are emerging, each one with its advantages and its drawbacks, and the choice is posed since one wants to build a Web application, a RIA (Rich Internet Application) having the same interface and the same possibilities that a local application as certain popular sites do it.
Fear to take the bad way and to spend months under development with an environment on which one could not lead while an other could have proven to be more adapted according post in forums where the question is very present.
Things seems even more complicated when one realizes that the various solutions suggested do not cease evolving/moving and proposing functionalities for now, and one wonders, will be it possible that in the future, such platform offers the possibilities currently offered by such other?

JavaScript and HTML 5

The new HTML 5 specification provides a universal interface for Web apps and some desktop apps thanks to the offline feature.

This is complemented by Ajax that is the combination of dynamic HTML (CSS, JavaScript, DOM plus the XMLHttpRequest object which allows asynchronous interaction between the browser and the server. And more recently by WebSocket and WebRTC for better interaction with the server or directly with other clients for WebRTC.
Applications uses server-side a scripting language like PHP or ASP or JavaScript with Node.js.

C# and XAML

XAML is like XUL an XML-based language of description of interface. It provides an interface language for Windows with .NET, on Linux with Mono and systems derived from Linux like Android.
It is used for the graphic interface of Windows since Vista, and by Windows 8 an 10 both in the new Modern UI/Metro platform or classic destkop with .NET.

See also: What future for XAML?

Java and JavaFX

The Java solution is complete since it proposes a server-side framework, and with at client-side, on the browser, applets, which are small applications functioning in a Web page. That can also be supplemented by a scripting server-side language, JSP. Let us add to that servlets for Web services and we have a portable and complete platform for enterprise Web applications. JavaFX helps to create user interfaces.

Qt and QML

Qt was originally a Linux framework for interfaces that has been ported on all operating systems including Android and iOS. It offers all the necessary widgets to build any interface and has also its own interface language, QML, which has a syntax similar to JSON and so is like JavaFX.

Summary table

The choice of the interface of Web application could be facilitated by using the following table:

Display in the browser
yes no
Portability on operating systems
yes Partial
Mobile compatible
Performance (reactivity)
Depending yes
Free of charge
yes yes
Too much complexity
no no C++ Java

Note that it is possible to combine solutions to solve the deficiencies of a format. For example, Ajax can be used at client-side in conjunction with Java at server-side to avoid the slowness of applets. There are also frameworks that allow to work offline.

Other solutions

The vector graphics SVG language allows to add graphical components to a Web application interface. Vector graphics allows widgets wich resize with the screen, and it is more appropriate for graphics applications and games, on the desktop. Web and mobile applications should not use SVG because the compatibility between browsers is imperfect.