Kiwifarms, I would assume. You’ll see why if you check out their Wikipedia article.
Go to the forums, do some searches to find threads on topics that interest you, and make your own decisions.
Just as the edgy comments are their “right to free speech”, I think it’s completely fine for XenForo to exercise their right to speech by not providing them service. It’s not like they’ve had their license revoked; they just cannot get support or software updates past when their license expires.