This is a very general question.
What do you want your website to do? Some CMS's have forum modules, and some forums have front page modules. I prefer to hava a website (using your own code or a CMS) and then have a subdomain (like
http://forums.mydomain.com) which uses forum specific software. It's a bit more management, but means you're not always trying to merge two functions.
Again, very general, and totally depends what you are trying to do. Do you have an example website that you're trying to replicate?