Web client development efforts are looking for RIA, but they need a server side support and the
glue codeaccording selected framework that enables you to loss a significant time in development.
The integration with gwt is basic for now in seam, but we wish it could change in a nearest future, so, if you need some restriction time, I recommend you to use the traditional seam application stack (facelets,jsf,ejb3,pojo,jpa,...). You can optimize the time response for the user using apache as web server;
But if you wish more good response times in the presentation tier, with a desktop-like pages, gwt or flex are good choice:
a) you can integrate flex and seam with exadel flamingo (as flex does with data services with another backend technologies, but flamingo does with remoting)
b) you can integrate gwt and seam with ... (the first approach is using remoting too, but see the jbpm's new console: it uses Rest).
Offline versions means that the framework where you work, should need support for save the state in somewhere (disconnected clients) that is not possible for jsf at this time; maybe adobe air could support this.