The two 747s are versions of the smaller model. An A380 would be a complete waste of space as well as being unable to land at all but a handful of airports. If the next Air Force One is an Airbus then it’ll be one of the smaller models, but I predict it’ll be a derivative of the 787.
Provided the 787 ever gets off the ground...as it is there are many hurdles to overcome...not to mention areas of the “carbon fiber” are de - laminating...rivited areas won’t line up so the have to be redone one at a time... the -9 version has been pushed back to a first delivery of 2013 this past week.
Several posts here:http://www.airliners.net/aviation-forums/general_aviation/
Personally if they think it needs to be changed I think the 777 is perfect
Except that a 777 flies under ETOPS rules. Do you really want the POTUS to have to make an emergency landing in Siberia?