It depends! Right now in 2013 Alaska by far it the largest. But long ago, Texas was once the largest.....so
Alaska is the now the officially largest state but before the Klondike King, Texas was the largest. Before Texas, Missouri was the biggest. Before Missouri, Virginia was the largest. Before Virginia, Georgia was the biggest. Before Georgia, Pennsylvania was the largest state in USA. And by default, before Pennsylvania, Delaware was the biggest state in America from December 7, 1787 until December 12, 1787.
It's kinda' not fair since for five days Delaware held all of the titles: the smallest, largest, tallest, lowest, coldest, hottest, smartest, friendliest, most populated, most north-south-east-west, etc...you name it Delaware has been there and done that.