Both are CO2. Mars's is too thin to survive breathing pure oxygen at the same pressure, so you need a pressure suit, besides, to go outside, and a big pressure vessel to live in. And, it is always colder than Antarctica, so you need to be heavily bundled up.
The cloud tops of Venus are at earth standard temperature, pressure, and gravity. The overabundant CO2, cracked, yields both breathing air and construction material. Sunlight, for power, is 2x as abundant as on Earth, and many moreso than on Mars, although the 50+-hour nights require more energy storage capability. An analog of geothermal power generation, relying on higher temperatures at lower strata, might be more practical.
The only particularly inconvenient details are access to metals, probably requiring asteroid mining; and getting there and away safely. It is quite tricky to shed enough velocity on the way in, and to get enough back on the way out.
A large orbiting ring with a radius that puts its circumference at cloud-top level, rotating at a rate that puts the lower rim at rest relative to the habitat, would go a long way to easing both arrival and departure. At the upper rim, its lineal velocity would be twice orbital, good for both capturing arrivals and flinging departures.
Face it, Mars is a dump. The smart money favors Venus.
You can't handle the atmosphere on Mars either though? Who cares if the lower atmosphere is toxic if you won't contact it anyway? It is like complaining about the atmospheric pressure in the Marianas trench.
The cloud tops of Venus are at earth standard temperature, pressure, and gravity. The overabundant CO2, cracked, yields both breathing air and construction material. Sunlight, for power, is 2x as abundant as on Earth, and many moreso than on Mars, although the 50+-hour nights require more energy storage capability. An analog of geothermal power generation, relying on higher temperatures at lower strata, might be more practical.
The only particularly inconvenient details are access to metals, probably requiring asteroid mining; and getting there and away safely. It is quite tricky to shed enough velocity on the way in, and to get enough back on the way out.
A large orbiting ring with a radius that puts its circumference at cloud-top level, rotating at a rate that puts the lower rim at rest relative to the habitat, would go a long way to easing both arrival and departure. At the upper rim, its lineal velocity would be twice orbital, good for both capturing arrivals and flinging departures.
Face it, Mars is a dump. The smart money favors Venus.