Rather Venus than Mars, which will remain useless. Too little gravitation to keep a substantial atmosphere, not much to make it from in the first place, too little water and nothing to extract more from, no magnetic field. Life on Mars will take place indoors only. One technology to clean Venus' atmosphere from C02 and thereby removing the greenhouse problem which isn't SF already exists, "artifical trees". We might possibly see millions of them soon here on Earth to fight our CO2 problem. There isn't much water vapor in % in it's atmosphere, but the value has to be multiplied by about 100, that's how much denser Venus' atmosphere is at the surface than Earth's. Enough to cover much of the planet with shallow oceans, it's whole landscape is as amazing and hilly as the American Midwest. The oxygination could reduce the surface pressure to 3 bar; dissolving nitrogen in liqid water, and binding oxygen in all sorts of stable compounds naturally would reduce it further. Still, the long solar day, and maybe because of it weak magnetic field remain.