Well, basically depends on the type and size of the application. If you application uses animation extensively then Windowless mode is not recommended since it will cause a performance penalty. For smaller applications, Windowless is fine. One tip I'd like to give here is: If you want to display a local HTML page in RadHtmlPlaceholder (i.e. use the HtmlSource property) then it is better to use our RichTextBox control instead of HtmlPlaceholder, since RichTextBox does not require Windowless. However, if you display an external page (i.e. you are setting the SourceUrl to some external url like http://www.google.com) then you should be using the HtmlPlaceholder since the RichTextBox does not support external pages.
I'd also like to hear of anyone else's feedback.
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