Right now I know of a company that needs to overhaul their front end. They don't have a lot of available developer resources and their core strength is backend (Python/Django). I'm sorely tempted to recommend Ember. Angular is in transition and the whole React circus would be overwhelming for them. Ember fits in very well with the Django philosophy and there are plugins to make them play nicely. Ember has a learning curve but it looks like it would pay off long-term.