Which forum software is the best??

For people with little to no PHP/JS knowledge I would agree Xenforo is probably the best since it has a large community with loads of addons and themes as well as an easy to use interface, but it's not the most secure in terms of vulnerabilities - because it has a quite a few 0days (exploits that haven't been patched since the initial release of Xenforo) and because at least 40% of forum on the web use Xenforo it's the most targetted by hackers. In other words your users are not safe.

IPS4 is also a very good alternative, if you haven't heard of it then I suggest maybe having a look. If however you know how to code in PHP/JS (HTML and CSS is pretty basic and doesn't really count as a web language imo) then I suggest you make your forum on something that constantly provides security updates like Wordpress or better yet, code your own forum software