What's your favorite forum software?

I'm hooked on Invision, which is what my 2 communities are using. I started with freeware called Phorum and when I realized the development of that software was dead in the water I knew we had to jump ship. I looked for who had the most supported and active development and it was a tough decision at the time between Xenforo and Invision but I chose Invision. I am glad that I did, because they are still taking the lead when it comes to security, innovation, and keeping up with the latest leading community software - which is definitely NOT Xenforo, Woltlab, nor VBulletin.