We're working to build the front-end of our application and struggling with selecting a good UI framework since we're not experienced UI people (we're mainly back-end developers). The central issue is that we don't know what we don't know and don't know how to best weigh our different options.
At the moment, we're evaluating Flex, ExtJS, and Vaadin.
Is there another option we should consider? What, are the major elements we should evalutate on? Any insight would be helpful.