I like the one by the south towers. Or near the resteraunt by the revolving doors on the first floor. Or if we wanted to be more scenic (with shade) there are stairs beneath the skywalk where I know Naruto cosplayers shoot a lot. There should be plenty of shade there in the afternoon if y'all want to do something outdoors.
(And is there a forum I can post the time/location so we don't overlap with another group?)