Bootstrap 3, Foundation, and more
In this video you will find out how quick and easy it is to get started with Bootstrap 3, Zurb's Foundation, or any other CSS / Front end framework with your Symfony 2 twig template based project.
There's really not a lot to it, though if I had to offer an opinion over which to go for, I would suggest using Bootstrap. This is based on personal experience - CodeReviewVideos originally used Foundation because I wanted to be a little different. However, I found a few problems along the way that made me change my mind and switch to Bootstrap. It wasn't a huge pain, but it wasn't a particularly quick thing to do either.
If you're in doubt, use Bootstrap.