Habitable planet

Has to be

Mercury - Mercury is a barren planet with little atmosphere. In many regards it is similar to our own moon. However, it is also very close to the Sun, so humans will have to set up bases in craters or near the Poles to avoid being blinded. It is extremely difficult, maybe even impossible, to terraform Mercury, considering it would involve creating an atmosphere on a planet with an almost non-existent one due to solar wind bombarding the planet.

Venus - While Mercury barely has any atmosphere, Venus on the other hand has a thick, toxic, and deadly atmosphere. The extreme heat and pressure would make it difficult to even stay for a few hours on the planet, since it is hot enough to melt lead and has 90 times the atmospheric pressure of sea level on Earth. In fact, the Venera probes launched by the USSR only survived for a maximum of 2 hours on the surface. Venus has also received some interest in terraforming, but though the idea is more plausible than that of Mercury, it will still be extremely difficult.