It depends what type of applications you want to build.
Although JSF apps sometimes fall into the category of traditional web pages this isn't necessarily a bad thing. Many web sites/applications don't need anything more than this. If you're adding Ajax to JSF you are still maintaining the server side template generation- the overall view architecture is still JSF.
GWT does not use server side template generation for its architecture but instead is run completely in the browser. The application communicates to the server through API's which are typically XML, JSON, or GWT RPC. This is a newer model for web application design which performs better and gives a good user experience.