What forum engine do you recommend?

Question

CMS

Advise, please, the engine for creating a forum. I used phpbb, but maybe there is something better from the free one. Maybe it's worth buying a forum engine (but the price is somehow expensive for me, I don't know if the forum will be promoted, while I think not to risk it)? For me, security is important so that the forum is not hacked. And to immediately release updates if vulnerabilities are found.