Which one you think is a tougher sport?
It depends on what you mean by tough.
NFL is tough in terms of physical contact.
NHL is tough in terms of how the hell does one even manage to skate and not fall down?
I once went to a skating rink when I was in elementary school, and I could barely stay standing up, even with one of those metal walker thingies and with someone helping me.
Ice skating puzzles me to this very day.