I would choose Miami, or if you are in St.Louis, go through DFW. I personally avoid Charlotte.....poor US Airways service, the concourses feel worn out / old and the Admirals Clubs are not great (the Club on B is in sad shape.....last time through there, the men's room was closed, the entire club smelled and the service at the bar was almost non existent). Miami's newer concourse is excellent (though crowded). Great shopping and the Admirals Clubs are very nice.