What a difference a year makes. Apple topped American Customer Satisfaction Index'ssmartphone rankings back in 2012, but Samsung has taken the lead in 2013 by a slim margin. Owners responding to ACSI's national survey gave an 84-point score to both the Galaxy S III and Galaxy Note II, putting the two Samsung phones just past the 82-point iPhone 5 and iPhone 4S. Researchers haven't explained the changing attitudes, although they add that the Galaxy S 4 and other newer phones didn't ship in time to count. It's at least clear that the American sentiment doesn't extend worldwide -- ACSI notes that South Koreans ranked the iPhone 5 higher than the Galaxy S III despite Samsung's home turf advantage. Apple also maintains the lead in ACSI's device-independent scores at 81 points to 76, although Samsung is quickly catching up. It's safe to say that neither smartphone maker can afford to relax.