luffys lifting strengh in his normal form is around 300+ tons (when he carried that golden ball) but superman can lift entire islands and mountains, also he is continually powered by the sun, his speed is also too much for luffy unless he uses gear 2nd - which cant be maintained for too long. durability wise they are both pretty tough, but supes can take a nuclear warhead, whereas don kreigs explosion spear managed to hurt luffy, even though he could withstand it, plus with heat vision, cold breath and super breath it’s no contest for supes, but still luffy is way cooler