In what major US sport is home field advantage most important?

During the 2007 (or 2007-2008) seasons, the NBA saw the greatest winning percentage for the home team, at 60%. NFL home teams won 57% of their games, and NHL and MLB teams each won 54% of their games. However 11% of NHL games ended in ties (there were no ties in the NFL that year, and the other sports don't have ties). The ratio of wins to losses was actually very slightly higher in the NHL than it was in the NBA, at 1.509 wins per loss in the NHL, and 1.505 wins per loss in the NBA.