Many have answered this question and many have asked me the same… So after research from various sites including and this is what I conclude:


  WPF  WPF XBAP Silverlight Ajax.Net
Client –
Windows XP SP2 & Vista Windows XP SP2 & Vista Windows XP SP2, Vista, Mac, Linux Any OS
Client –
.NET 3.0 .NET 3.0 Silverlight Plugin Not required
Client – Browser 

NA Internet Explorer 6+ FireFox, Mac Safari, Internet Explorer Any Web Browser

Downloadable Installer or ClickOnce Runs in Internet Explorer secure sandbox One-time install of Silverlight plug-in Web Page
When to use Programs that need access to Windows desktop files. Intranet applications for Windows-oriented companies. Rich Internet Applications for public-facing web sites General-purpose public-facing web sites 


Disadvantages Typically works on MS-OS only Mostly internal sites for companies that use MS-OS. Works on any browser but has limited functionalities compared to WPF, WPF XBAP Lacks Richness in UI

Guess this will be helpful in analysing situations where to use what!