Recently I designed a game for the decktet, Solo Hex. I posted it one the Games Design forum, without realizing there was a new games forum. The descriptions for both forums seem pretty close, so which forum should I have posted it on?
Well, nothing is written in stone, so you should do what you feel :) but initially I thought the games design forum as a place to post ideas, drafts, etc… for discussion and testing, or just questions about design. The new games forum is for posting about new games that are added to the wiki.
At some point (whenever you think so), you might want to add your game to its own wiki page, so it is listed on the wiki pages like All the Games or Games listed by Category. To do that, just use the "Add a new game" form on the sidebar to create a new game page and fill in the template.