There's another completely pointless arguement, what the "hardest" sport might be. Any given sport is infinetely difficult, and mastering a physical discipline is completely impossible regardless of how or how often you train. All you can do for arguements sake is compare the playing field and what level of athletes currently take part in a given sport, and anyone who would make an arguement that boxing or MMA currently is anywhere near the top here needs their head checked as far as I'm concerned.