Having played both (granted, only at the intramurel level), here is what I think. You'll get a helluva lot better cardiovascular workout playing rugby. The whoopee game just never seems to stop. Also, there is *more* hitting in rugby, but it is a lot less violent. Rugby, in my opinion, is kind of like a mix between soccer and football (U.S. style). Football is a tougher game. You've got to be bigger and stronger to play football competitvely, compared to rugby (in my experience). People are looking to to take you down, and they are looking to take you down *HARD*. You might think that the only people that really get hammered are the wide recievers, running backs, and quarterbacks. Not true. You come around your end blitzing the quarterbacks blindside and a tackle pops you in YOUR blindside, and you feel it. I've hit the ground so hard that my teeth clicked (well, they would have but for the mouthpiece).. and thats on DEFENSE.
I saw a fair share of broken bones and other assorted injuries, but they tend to be a lot more severe in football. You'll get broken fingers, broken noses, maybe a ripped ear (which is rather disgusting to look at) playing rugby. I never SAW anything more harmful than that. Even playing at the intramural level in football, I saw a kid break a leg, a couple broken ankles, a buttload of hyperextended knees, a couple broken wrists, and other more minor injuries (sprains, pulls, etc.).
There is a reason that there are ambulance crews standing by at all college and pro football games.
