Certainly there are some team aspects to take into account, but I've worked on several projects as the sole developer with multiple (3-5+) non-technical stakeholders, and Trello has been the best for that setup. Commenting is intuitive, even folks who've never used Trello before understand the columns/swimlanes reasonably well, and it's usually pretty easy to get them to attach documents, provide feedback, etc. all within an individual card.