In a nutshell, if you're about to propose a new feature with adding some totally new functionality to `bowser`, it's better to branch from `master` and make a PR pointing back to `master` as well.
If it's a small hotfix, fix a typo in the docs or you've added support for a new browser/OS/platform/etc, then it's better to branch from `production` and make a PR pointing back to `production`.