MMA & Hockey, my two favorites... the US is just a baseball, then football culture... its just so ingrained in our history that nothing will ever bumb it. the huge support for basketball by minorities and non-minorities alike will always hold it above hockey, which, inarguably is a white/canadian/easter european sport!
also, its alot harder to play hockey when your a kid. you need to buy a stick, pads, skates, and learn to skate. sure you can have foot hockey... but still, need sticks and a few balls... and nets... basketball... well, all you need is a ball. football... only a ball...
as for baseball, well, its america's pastime!!!