I'd have to say that they are both great, though I'd have to call American Football my favorite.
I played Am. FB for 14 years and soccer (fb) for 5, and I know that there really isn't any grounds for comparison other than they are both exciting sports. I have to say that I found American Football to be more physically demanding and draining. Both are exciting and challenging sports, and neither should be subject to demeaning.
I have to say that I also love Baseball, a sport you really have to know to be able to fully appreciate, and hockey. Let me tell you, I was a hockey goalie for 17 years and nothing came close to being as physically and mentally challenging.
My 2 cents...
OCWIATJ Forever