We have a dedicated page for Epics which lets you prioritize epics against each other, which basically provides a high-level priority that anyone in the company can look at to get an idea of what the next few months look like. We're also working on building roadmap support to make epic dependencies/order more explicit.
We currently use Trello for project management but find that the duplication of data between Trello and GitHub and the lack of "higher order" views (epics, roadmap, etc) make us want to move to a more purpose built service.
