I played Soccer for 10 years, and just finished my 6th year of football so I think I have a pretty good opinion about this.
Football requires more from your body. It requires more athletisism, and no matter what you say, the collisions in football are WAAAAAAY bigger than anything in Soccer. I was a team captain for 4 years, MVP one year, playing Middle Fullback for 8 years straight and having the repuatation of being very physical (some people thought I was dirty but I very rarely got carded)
The thing about soccer is that it's about 3-4 times more tiring than football, but two days later when you're still feeling those football bumps and bruises you'll know what you gave your all to. In soccer you feel dead tired and your legs feel heavy. Football depending on your position (I'm just a WR and gunner on special teams) you will feel like hell. Go try playing runningback in a competitive league for ONE game, good luck, I can't. I'd be murdered at my size. Soccer each position is not marked by your height and weight, and is less of a chess match, but it is still one of the best sports ever created.
Soccer requires more skill, football requires more athletisism and a combo of speed/power.