As far as I know Guvnor is being refactored to remove all the EXT-GWT code that it's in there. the same is happening with Wapama the process designer tool.
Google is making huge investment in GWT and that sounds like a secure bet for the future.
I think that using plain/pure GWT will be better to not be dependant of third party framework that can change the licensing when they want.
Once you learn GWT we can create whatever component that we want, most with the new versions that are including more and more ways to create smarter components.
My two cents..