There are no moons larger than Mars. Titan (Saturn's moon) is the largest in the Solar System and is smaller than Mars. However, Titan has a thick atmosphere and has oceans of liquid hydrocarbons. Our moon is only about half the diameter of Mars.
I doubt if humans will ever go to Mars. During a journey that long it seems they would permanently lose muscle mass due to prolonged weightlessness and, it now seems, would experience dementia from exposure to cosmic rays. Increasingly, robotic craft could do anything humans could do much cheaper and better.
