Highly personal (and probably biased) view: best framework == no framework.
Can't agree more....
Best framework = your own brains... ;)...
Every situation is different, so the frameworks don't fit 100%.
Use them as examples: Look and Learn.
If you have a good understanding of the GUI patterns, you don't need this frameworks and setup something yourself in "minutes"
My experience: the activity/place concept in GWT is nice for simple app's, but not for bigger app's. I tried it, it doesn't work.
I use something similar that is a combination of the state- and visitor pattern, and works very well to realize flow's.
- Ed