MS Planner is known to have a progress field, while Trello only adds configurable labels. It depends on your business requirements and preferences. Configurable labels of Trello are sometimes very suitable for small projects, and progressive field by MS planner suits large enterprises the most. Both platforms offer attachments even within the card, and Trello allows individual comments. And both are very helpful for sharing multiple documents at a time. So, all you come down to your business model, requirements, and other preferences.