Rugby sucks. Yes I have watched it as well as Australian rules football. In whiny Australian voice "but we don't weeeeear pads" - exactly (because you dont have to) it is glorified soccer. I couldn't name one rugby player for a billion dollars. I would say 99.99999% of Americans couldn't name a team / player / league / how much a point is worth with a gun to their head.
I'm American, just figured I would say that before I say my piece.
I played both competitive Rugby/Football in High School.
To begin with, you can't really compare the two - Football is about power and speed, with some technique. Rugby is about technique with some power and speed on the side. I say this because in Football you can basically tackle someone any possible way (other than face mask/horse collar) without a penalty. In Rugby on the other hand, you have to wrap up and make a "legit" tackle, or else it is a penalty. This is the main reason you don't "need" pads in Rugby, because if you don't tackle properly (also the proper tackle in football) there is a smaller chance of getting injured.
Despite saying this, I will list my injuries over my two "careers" in both sports:
Football - 2 Knee Hyperextensions
Rugby - Too many Knee Hyperextensions to count, too many ankle sprains to count, 1 concussion (I actually did this to myself, got hit awkwardly and somehow managed to knee myself in head), and 1 partially torn MCL.
Cardio-wise: Football can't even touch Rugby. You get maybe a 30 sec break every 5-10 mins. You also play both offense and defense, so there isn't much time to stop thinking/moving.
I love both sports, but you can't argue one is "better" than the other. We, as American's don't really play Rugby, and they, the rest of the world, don't play football.
Sorry to not mention Aussie Football, but I just wanted to throw that out there, and I don't really know all the rules to it yet either.