Daniel sent me his comparison of indirect AJAX programming frameworks for ASP.NET. As Ajax.NET [1] is a framework where you have to do JavaScript programming other frameworks allow you to use AJAX stuff simply by adding some configuration to you web.config or by inheriting from a special page class.
See the comparison of AJAX frameworks here: http://www.daniel-zeiss.de/AJAXComparison/Results.htm [2]
Note: Ajax.NET Professional has some prototype functions included that are not needed for all the calls (i.e. HelloWorld example). The client scripts are cached locally so you will have only a initial higher traffic. Daniel will add more diagrams that will show how the frameworks can be compared with multiple calls. As Ajax.NET Professional [3] is a framework for advanced users it will have the smallest traffic.