Would it be easier to terraform Mars or Venus for human habitation?”
Venus has a lot more to work with than Mars. It has a lot of CO2 in its atmosphere, and algae could be seeded in the air to convert the CO2 to oxygen, which then could be used to form water and so forth. The biggest problem is that it’s 25 million miles closer to the sun, so it’s going to be hot, but it’s possible it can be made habitable. Because Mars has so little gravity, it’s difficult to hang onto its atmosphere and it drifts away from the surface over time. It might be possible that water trapped in the planet could be liberated and an atmosphere could be created, which would also warm up the planet. But I think it would be much harder to terraform. I think the best you might get is being able to pressurize valleys and people could live there, or underground.
