It's "winning", since people will continue to post for a long time...but I guess no one puts thought into Forum Games. :(
See, all you need is the last post. You don't even need to say you've won, the title already tells the reader that.
MSN:
[email protected]His Royal Highness Utterly Awesome CoW I, who rules over the City of Wonder, posted the last message of 2009 and is now known as Mootilator.