On the Symfony Finland site there's a new post with some suggestions on choosing a frontend for your Symfony-based applications according to your needs.
They talk briefly about the history of the framework and what kinds of considerations should be made for both the front and backend technology. They also remind you that there's not a "one size fits all" frontend technology out there. They describe a few different kinds of situations (backend heavy, frontend heavy, etc) and make a few suggestions as to which way you might want to go and libraries to investigate.
The next time you're faced with starting work on a front end of a web site or web application built with Symfony, you can reflect on the experience you've got from the back end. There are usually many right answers and no absolute truths.