I would say that there is no "best" forum system out there, since it all depends on what you need it for. So, at the end of the day you decide what's "best" for yourself. Every forum has pros and cons.
However, for me flarum is definetly the best forum I ever had. It's just so intuitive and fast, which makes it fun to use. Not to mention that flarum has the most beautiful mobile view you could ever get. It just looks amazing.
Of course flarum might not be the best choice for a big community right now, since it's still a beta (duh!). But as soon as it's finished, I know it will be even more amazing. And that for $ 0.00 .
