(By the way, for Americans: 'Rugby' means 'Football'.)
Rugby and American Football are two completely different games. Although they share a lot of principles they can't be called synonyms for each other. I play American Football over here in the states at my school and all the padding keeps you pretty safe, but you still get battered a little every once in a while. Rugby players tend to brace for impact more than American Football players, so I guess that helps with your decision.