1) My personal favorite is the Carpenter Clay Guida. There absolutely is no quit in that guy. From bell to bell he is bouncing around on his toes. 2) Either Diaz brothers. I have never seen either of them gas and they seem to build up steam as the fight lingers on. 3) Cain Valasquez, his cardio is legendary, which is remarkable for man his size. Honorable mention: Roy Nelson, he never stops, just keeps charging forward, which is interesting to see from a fat man. Yes, he does slow down, but he never stops. And while he may slow down, can you imagine how good his cardio must be while carrying all that extra weight. Imagine who good it could be if he was carrying 40 less pounds. How do you all think has the best cardio and why? Edit: I totally forgot about Joanna Champion. She is another one who just seems to build up steam as the fight goes on. She really shines during the championship rounds and turns the heat up in the 4th and 5th round.