One thing to keep in mind here is that the DSF is not running the Discourse instance - we’re using the hosted version. (Unless something was changed that I’m not aware of.)
From what I can see, there is no hosted Misago provider.
So what you’re looking at is an “apples to oranges” comparison. The DSF definitely doesn’t have staff to manage a forum, so I don’t see where Misago would be any kind of viable option. (I’m going to guess that I’m probably still the most active staff member here, and I know that I don’t have any desire to manage it from a systems perspective.)
Honest answer is that you should go with the software you like the most and that meets your needs the best.
Discourse is a business - they have a team of developers constantly working on it.
Misago is an hobby project developed because I run a few forums myself and I am not happy with existing OS forum software + I am Python dev and would like a forum in a tech stack I am personally familiar with.
Its granted that Discourse will be more polished and featured option than Misago. But at the same time, Misago aims to have a more vanilla forum experience to the users - this big switch didn’t happen yet but its coming sometime this year.
If you are a business and dont want to bother with technicalities of your community software, Discourse will be a better option, at least for now.
If you are a hacker, hobbyist who wants to fiddle in Django, and/or preffer a forum software closer to, say, XenForo or Invision Community, but also open source and free, even if it means odd quirks, lack of polish and some missing features, I would go for Misago.