American football and rugby are both physically demanding sports... I've played both... The styles of play are much different though... Rugby is about pure tackling and ball movement as opposed to football which is about impact in addition to tackling skill and quick linear movement down field. The speed and impact in American football is the reason for the pads (without them, the amount of spinal cord and brain injuries would be horriffic)... With regard to the breaks between plays in football, there's a purpose other than giving the big guys on the lines a break (and by big, I mean 300+ pounds...). American football is a game of set plays and tends to get very complex with all the terminology and the amount of plays you have to memorize (most coaches script anywhere from 150 to 250 possible plays per game). Granted, rugby is more fast paced and the plays are more oriented to the flow of the game which makes it pretty exciting to watch and challenging to play. As far as I'm concerned, they're both great sports with their own challenges.
Would like to get your ear ripped off in a scrum or have Roy Williams crush you coming over the middle playing American football?!?