Is it too obvious to point out that football players only play, at most,17-20 games a year and only once a week? I'm pretty sure the average nfl'er takes way more of a beating than any nhl'er.
But, the question was "who hits harder". I don't know. I do remember whe mike sellers played in winnipeg (cfl) the paper ran an article stating that taking a hit from the the 280 fullback was equivalent to jumping out of a three story building. ouch.