I am a fan of Australian rules, Rugby and American football and have played 2 of the 3 - American football through high school and rugby on my university club team - the University of Kansas which had, and still has, a strong collection of rugby clubs which play nationally and internationally on occassion. The games are different, as the links show, and are popular for many reasons. If you truly think that the 300+ lb linemen in the NFL are fat and out of shape slobs with no athletic ability you are sadly mistaken. Can they run a marathon - or even a half marathon for that matter - no. However, I'd wager you'd be quite surprised at how quick and agile these big me are on the NFL level. Their role is to maul the other line to enable the "skill position" players to execute their roles and often lead the running game which requires great speed and athleticism. I loved the action and brutality of rugby but, in my opinion, the strategy of building a gameplan for a set piece contest and making adjustments during the game is great fun in the American game as well. The term "football" may be common but the games each have their nuances which appeal to different groups and saying one is better than the other is an argument which will never be resolved to which you agree.
I don't claim American football is the best but I will say I watch Australian rules, rugby and American football regularly. As for "world" football (soccer), I only watch it because my son is too young to play the American version which he craves. Aside from watching my son and his pals... soccer can remain a sport this crass American cannot appreciate especially when "action" is a requirement.
(wow, the new smilies allow me to access my juvenile humor, hehehe).