Apart from the argument of Wicket\'s simplicity (that is, Wicket is a simpler system IMHO) and GWT\'s responsiveness in the client (GWT\'s client side state and JavaScript -
The genius behind GWT is that you work solely with java. They did a great job with RPC making it almost transparent to the programmer. A lot of times you feel you're coding more like a desktop app instead of an application with a truly defined client and server side.