Comparision: JSF AJAX Framework vs. JS Framework and Web Service

I'm in the middle of a decision phase of how I should design my next AJAX-Single Page Web-Application.

At t开发者_开发百科he moment I have reached crossroads.

Should I go for a JSF AJAX Framework (like IceFaces) or should I use a JS Framework and build a Web Service which the JS Framework can comunicate with?

What are the major advantages and disadvantages of each approach? When should I use one or the other?

The most important factor to consider is: people. Both strategies is interesting and tecnically ok. So, if you have people with knowhow to work more confortable with one option or another one thats is the best for you.

should I use a JS Framework and build a Web Service which the JS Framework can comunicate with

What about the performance?

Why not consider GWT?