Why not both? We use vagrant to create our docker environment - a 3 machine CoreOS cluster. This is so we accurately represent our production environment.

We then use our production docker image(s) with some more development appropriate configuration options. Vagrant mounts the user's home directory at /Users/<username>/ inside the CoreOS machines. Then we mount the appropriate folder inside the docker container at where the container would normally expect to find the app's code. This way the developers have live updates without having to rebuild the docker image or anything.