Humanity is so smart that it can't figure out how to ration petrochemicals or decide to use nuclear power to solve an incoming energy crisis, but it can somehow colonize a solar system.
One, two things that are so simple that multiple groups of people decided they were both good ideas and executed them with varying degrees of success (occasionally doing both, but mostly just either/or), and the other: a task so infinitely more difficult than all things previously done before or mentioned that we've not only never done anything close to it, but have seen no evidence to suggest it's possible in the first place by anything in existence in the natural world.
Okay.
By the way we're talking about mammals that stop breeding the second you introduce them to air conditioning and microwave ovens.
It's one thing to say "I can make an airplane". You can because birds fly. Birds are powered flying machines. They fly by flapping wings with motors and they are small so they are probably weaker than people. Plausible but will require evidence.
It's another thing to say "we can shape the world to our desire" as the wet dirtball that same set of mammals lives on is being increasingly polluted with particulate aerosols, plastics, and noxious chemicals, and while people are independently deciding this is bad and needs fixing, no one is able to pull together enough clout to stamp down firmly and say "we need to do this".
One is a plausible and reasonable deduction that requires observation of the natural world to confirm, much as how Newton observed the movement of water across rocks in a river and developed the concept of Newtonian fluids. The other is a religious delusion that elevates man's unique tool solving ability to be comparable to nature itself, despite all natural evidence suggesting the contrary.
If we're considering mega scale architectural capabilities on part of humans to shape the natural world in the celestial sphere, then Venus is still the better option. Because there's no way to make a planet have more gravity without making it bigger. That 0.3g is really gonna hurt the descendents of Martians who, at best, would turn into non-human subspecies in a few hundred or thousand generations. At worst they wouldn't exist. Venusians would likely be somewhat swarthier lads, but otherwise human, though. As far as anyone knows the slight differences in gravity between Venus and Earth likely wouldn't matter (maybe they'd be slightly taller too).
Which is important when we're talking about species survival rather than life in a panspermian sense. Gravity is the real killer at the end of the day but the soil is also crummy. I would prefer Venusian algae farms in all seriousness, and maybe the acidic salt lakes can be fixed with starter cultures of carbonate producing bacteria, that can be fed to oyster farms, to provide a native calcium economy that would reduce dependence on Earth.
If the point of a colony is to eventually be totally independent and totally backup to the original home planet then Venus is your only shot. It's just Earth's younger, more tsundere twin.
tl;dr Mars is inherently bad for Earth life. Venus is also bad but less inherently bad since it's similar size to Earth. These are the most important attributes. If both have breathable atmospheres, there's literally no reason to go to Mars. Ever. Even if they both have crummy soils Venus wins every time. The only reason people like Mars IRL is because of KSR's books and because it isn't covered in a noxious atmosphere of sulfuric acid and massive pressures like Venus.
Apparently it's easier to imagine making Mars geologically active than it is to imagine putting a solar shade in front of Venus and seeding it with iron or ice though. Maybe it's because people have no sense of scale for the difficulty of the former. One is orbital mechanics and the other is something so (literally) hard we don't even know what the mantle looks like, and people think that low gravity doesn't affect them or doesn't have severely detrimental effects on human physiology. Lol.
