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In theory, I can think of a few end states for Mars to orbit at same or similar distance to the Sun as Earth does, for example putting Mars in Earth's opposition so they're co-orbital with Mars roughly where L 3 would have been if Mars wasn't there, or putting Mars into a 90° or 270° inclination orbit that intersects Earth's in opposition, or ...
Venus' surface gravity is much closer to Earth's than Mars' is, so the long-term health effects of living in a low-gravity environment are likely to be less on Venus (if they are even a problem there at all) compared to Mars. You also get the benefit of Venus' atmosphere for shielding against cosmic rays and radiation from the Sun. TL;DR
Following @gerrit's advice, here's a plot showing the relative difference between the distances Moon-Mars and Earth-Mars. The envelope of the curve oscillates between ±0.089% (during conjunction, when Mars is the furthest) and ±0.69% (during opposition). This difference is positive when Earth is closer to Mars than the Moon.
Launching from Mars is far easier than launching from Earth or Venus. A spacecraft that can launch from LEO and land on Mars can easily have the propulsion capabilities needed to launch back to Earth for another mission, if it can refuel on the surface. And Mars has the raw materials needed to produce propellants. Habitation:
Venus is also closer to Sol than Earth - figuratively downhill that is. All three bodies (Venus, Earth, Mars) being in motion there may be occasions when Mars is perhaps physically closer. Yet Venus appears to have the following advantages - Further downhill in the Solar System; Masses almost the same as Earth; ergo larger sphere of influence
According to this planetary temperature calculator, an Earth-like planet (similar albedo and greenhouse-effect atmosphere) at Mars's orbital distance would have an average surface temperature of -40ºC as compared to Earth's 15ºC. We can check this; Mars' semi-major axis is 1.52 AU, Earth's average temperature is about 288K (15ºC). So we expect:
There's several advantages and disadvantages to Venus compared to Mars terraforming and colonization: Advantages: Venus's gravity is ~0.9 G which is very similar to Earth's; Venus is closer to the earth with less communication lag and more frequent launch windows (around every 600 days instead of 800 days to mars)
But Mars' atmosphere is extremely thin, just a few hundred pascals. If the solar wind can do that all the way out to Mars, which is 2.1 times farther than Venus...then what is Venus doing with all that air? Some things I tried to think of that make Venus different from Earth or Mars: Venus rotates extremely slowly. Venus rotates in the opposite ...
previous answers provided an insightful answer by pointing out it is the mass of the atmosphere which provides pressure. But this begs the question of why Venus’s atmosphere is so much more massive than Earth’s (Venus’s sister planet). Or, conversely, why Earth’s is so much less massive. Most of the difference is due to CO2.
Venus, while having lost little nitrogen due to its size, is even more water-depleted than Mars; Mars has a 5-7 times higher D:H ratio than Earth, while Venus has a 150-240 times higher ratio. It's amazing and kind of sad to think about how Earthlike Venus used to be.