If you consider only job market , you should choose JSF. But, I belive that the future of RIA belongs to GWT and gwt like client side technologies.
I think that the most obvious upside of GWT, it is better scaleable than server side presentation layer technologies such as JSF, wicket. Because , server does not need to store client state and the client cpu power also are also used.. It is a huge benefit, you dont need to serialize client state between server computers to achive fault tolerant system.
