Well, I'm Brazilian and as a football fan and also American fan I must say there's space for both in the world. Each has it's strenght and weakness, but are they both are pretty cool once you understand the game.
I still think that american football is better played than watched, since good plays are actually rare in it's 3hrs length(yes, unlike someone said before, a match can take 3hrs with all the interruptions that are actually part of rules of the game.), but at the same time is wonderful to see a well done play.
While football is just awesome. If you take the time to watch some PELE videos or even Ronaldo's(the real one and not Cristiano) at their best moments, you have to fall in love and the beauty is that I watch similar plays while playing with friends in a rented field, while is quite difficult to watch a 100 Yds pass in a amateur match, you have to watch a American College game or a NFL one for that).
But there's no superior sport, just a more liked one given cultural reasons.