I prefer IPB but it is to costly to have to purchase a licence for it. But the alternative for me would be phpBB which is free and similar from softaculous if you have it.
Never heard of Flarum before. Must have been living in a cave. Looks interesting.
I've been tracking Flarum since forever and have even considered it as software of choice for HostingDiscussion during migration from vBulletin a few years ago. Back then it wasn't very stable, in my view, and I realized the community wasn't big enough to produce interesting add-ons.