Like Starcraft 2 or Supreme Commander 2. Because a game like this when it comes to multiplayer functions much more like an RTS than it does an FPS. People dropping = you're losing. We can't have players joining and leaving when how long you've been in a game is a factor. You'll have more skills and money for example.
I would like to mention L4D2 as the textbook example of pc lobbies done right. I don't expect such a hillariously large offical/fan maintained server support though, so we'll see what'll turn out to be the best solution.
