@PhenomX6 Discorse seems to be the most popular because it supports AJAX. Even if the interface is too bloated for some. It does have an API so it is possible to create alternative front-ends to it.
One friend of mine is making his own MyBB fork. I'm not sure if that's a good or bad idea. I'm staying away from Xenforo after the licensing fiasco and the fact it's paid bullshit.