See the comparison of AJAX frameworks here: http://www.daniel-zeiss.de/AJAXComparison/Results.htm 
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  is a framework for advanced users it will have the smallest traffic.