Welcome as US interest in rugby is, I can't help feeling that if they became significant, they'd ruin it with demands for breaks in play while the TV shows the adverts. To my taste, American football is too broken up to be very interesting: every play is a setpiece, and the plays separated by breaks so prolonged that the players have had time to recover before the next (assuming the lineup hasn't changed completely). Rugby has much greater posibility of a sudden, unplanned change from attack to defence, and also requires the strategic conservation of resources- too keen early on, and the team might be scraping the barrel by the last quarter. But de gustibus non est disputandum.