I worked with Trello for a while and was very happy with it because it is platform independent. This makes it easier to work with people who don't have direct GitHub access, such as graphic artists and designers.
Personally, however, I am currently more inclined towards quire.io.
The reason for this is the provision of 'organizations' as a superstructure and a project-specific overview via a dashboard.
Thank you for the feedback! This is right, github is a platform for devs mainly and if a team has non-dev people involved in the project it might be a strong reason for choosing Trello.
I've never heard about quire.io, it's time to check it out...
It is relatively young in terms of duration and they are very open to feedback. So I could achieve through my feedback that they allow and display checkboxes for the descriptions of the tasks as markdowns. And this within a few days.
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