I liked discourse for ease of use and simplicity. There's an active community though I personally find their release methodology a bit annoying. Aka. our forum is pinned to a release which they don't recommend. But at least this way if something breaks it only breaks on each release instead every time they feel like pushing a patch that breaks shit.
If you're self hosting, I'm generally more interested in maintenance, updates how to manage that and of course if it's usable to the user. If you're doing things that go against the 'defaults' in any software you usually spend time not worth it. Aka. the dark theme used to be hacky cause things kept on changing, now I think they have a supported one.
I also can't stand the 'classic' looks of forums, so I have my biases. The other two I was looking at were: https://flarum.org/ and https://nodebb.org/. Both of those have a more modern feel/ look. They all plugin support, themes etc...