I have to say the Soapbox, but that doesn't mean I always make posts there. According to my profile, the largest part of my posts are made in Games and Humor. I have to say that I also spend some time in the Mod Forum as well, though maybe not as much as Cia and Jan. Mostly I end up in chat, but I almost always have another tab open to the forums, often to see what's new in the Mod Forum, the Writer Support Team forum, The Soapbox, or Games and Humor.
@ Dannsar- Actually, you wouldn't want to be a fly on the wall in the Mod Forum. Some of the idiocy being talked about can really get on the nerves, especially when there's spamming or people being naughty in chat or The Soapbox.