DOJO - this library differs significantly to jQuery, in that it encourages the developer to create classes and custom components (called Dijit's) from the start. So in terms of the 'programming model', DOJO win's hands down. Where DOJO is not so great (and I was using version 1.5.1 on a legacy browser IE 6), is that some things are hard to do, such as styling a button. Why is styling a button so hard? Well DOJO nests the button in a load of div's or span's (I forget), and each of these layers has a css class associated with it.
See: Style Button for more info about styling buttons (although I do not recommend this method, it does highlight there can be difficulties doing such a simple task).
The upsides of using the Toolkit are that it is going to work well with Google API's, Map's, Calendar's etc... It still does not seem to have taken off quite yet, a jobserve search will show not it's future is still uncertain:
So, what would I use for RIA?
It would depend on how 'rich' it needed to be:
- If I was trying to write a web based application with some widgets enhanced, I would choose Spring MVC with jQuery.
- If I was trying to write a really whizzy rich application, I would choose GWT.
The Play Framework looks interesting, but the increase in volume of their forum has not carried on the trend of the previous year:
Play Framework Forum
however, google trends shows there is more interest in it: Play Framework Trends
Of course, if there were graphical elements to the application, then this would bring HTML 5, Adobe Flex and Silverlight into the mix.