G4JSF (JSF wrapper around GWT) worked fine for me.
except for internationalization that time GWT internationalization was poor,
I read some where they have fixed the problem now. but haven't test it.

I used several other JSF Ajax enabled framework and all of them worked fine for me
except in cases that they had to be used in portals.
looks like they are fixing Portlet and Ajax conflicts in JSR 286 (Portlet 2)