That's a great question and answers will very due to subjectivity. I personally think, in terms of being athletic, basketball players are the greatest athletes on the planet. There are plenty of players in the NFL who were collegiate basketball players (Antonio Gates, Julius Peppers, Jimmy Graham come to mind). I think it's a matter of opinion. Then there are the NBA players who were influenced by soccer - Steve Nash, Jason Kidd, Kobe Bryant, Luca Doncic, Leandro Barbosa. I'm sure there are others. Maybe Messi played another sport, but I doubt it. Can you imagine Lebron James playing the 9 or the 4? He's an incredible athlete and likely could have played in the NFL.
The list is open to debate of course. Toughest athletes on the planet? --> Cyclist on the Pro Tour.
My point is that in the US, the athletic kids gravitate towards the sports on TV, the sport where they can idolize someone. Not too many kids in Milwaukee know who Michael Bradley, Jozy Altidore or Clint Dempsey are. There are some kids who do, but most kids haven't a clue.