Of all the other planets in the solar system, Mars is the one most like Earth in terms of the ability of humans to live there. Venus is closer in size and mass to Earth, but its ridiculously thick atmosphere of carbon dioxide gives it a surface pressure 90 times Earth’s and a runaway greenhouse effect that would soften and/or melt the metal in a housing structure. Not to mention the sulfuric acid rain.
Not that Mars is hugely better. It has only 0.6% the atmospheric pressure Earth does, so standing on the surface without a pressure suit is the equivalent of trying to breathe 30 kilometers above Earth’s surface — three times higher than jets fly. You’d suffocate before you could freeze to death in the frigid temperatures there.