Left 4 Dead fan film features some surprising cameos

This is the full length version of the Left 4 Dead fan film that was teased two weeks ago . With Bill's tragic demise, the Left 4 Dead crew are a member short. On the way to a safe room three blocks away they find a replacement. And then another one. And then another, until everything's gone a bit mad. Which one would you pick to become the crew's new fourth member?