Plant cultivation is far, far harder on Mars, for many reasons.
1) Natural light: the solar constant is 1/5th as much on Mars as on Venus, and you're guaranteed to have dust clinging to your greenhouse glazing. More on this later.
2) Electricity: Same for solar power. And fission power systems (as opposed to radiothermal, which is far too weak) are 1) a rather expensive line-item to your development costs, 2) heavy to transport, and 3) complex (complexity is not good when it comes to operation in space). Beyond this, most people vastly underestimate how much power it takes to grow plants under lights - you need 1-2 orders of magnitude more area of solar panels than the area of plants you can grow. And the size of the LED lighting systems you'd need is very significant in its own right. Plants consume way more light to grow than most people give them credit for. The real world isn't The Martian where one can grow potatoes on normal room lights ;)
3) Room: Abundant, practically unlimited space comes free with a Venus colony. Space is extremely expensive on a Mars colony - it's a pressure vessel. Another downside to limited space: plants don't like it. It leads to humidity and temperature instabilities and buildups of gases like ethylene that are far more poisonous to plants than carbon monoxide is to humans. These gases break down, particularly in sunlght, so in big areas they're not a huge problem - but in confined spaces, they can deform and kill your plants readily. Pests and diseases also thrive much more in confined spaces.
(My comments on plants come from experience: I grow a small "jungle" in an indoor environment, entirely on artificial light)
So, while it is of course possible to grow plants on Mars, it's far, far easier on Venus.
As for opressiveness, once a wall is opaque, you can't really perceive how thick it is.
Indeed, I wasn't talking about wall thickness :) Just the issue of being enclosed in small spaces. Most designs call for integrating as many windows as they can, but that's always going to be limited - windows are a lot heavier for a given amount of surface area and can't be shielded for radiation exposure.
And I'm not sure how attractive Venus would be in comparison
So, you don't get a landscape, that's true - the surface isn't visible there. But at the desirable altitudes, there is still a "view", the clouds are dynamic there. A few kilometers further up and it's just a continuous haze (which may lead to rainbow effects below, there are some papers debating this ;) ), but in the "earthlike" layers clouds will come and go. Like living among the clouds on Earth.
But no, you don't get a landscape outside. Your landscape is the Garden of Eden you make inside, surrounded by clouds. :)
There's also those ever-present lightning storms all around you - that's going to be noisy, and a serious maintenance issue
The current state of research isn't "ever-present lightning". Again, unfortunately our knowledge of Venus is so poor compared to Mars, so it's hard to make definitive statements. But lightning appears to be "about" as common on Venus as it is on Earth.
Another thing that we need to learn more about is atmosphere variation. We've seen what appears to be significant variations in sulfur levels on Venus over time - it seems that the sulfur may be the result of frequent or continuous volcanic activity. So how the atmosphere will vary over time is an important question to be able to answer before we can send humans.
And how do you plan to prevent lightning strikes through your habitat?
Again, we don't know the distribution of lightning between a) different altitude layers, b) different latitudes, and c) over time. We actually don't know at this point if it's ever a risk at all - and if it ever is, whether it's avoidable or not. If it's not avoidable, then yes, one would need lightning protection (I presume faraday cage-style rather than any sort of ion shield), which would add mass and require a more difficult testing regime. If it is avoidable, or is never a problem: then there's no issue.
Definitely need more data on this one before we can send humans! It's time to stop neglecting Venus.
but since you're in the middle of the cloud layer they won't actually be getting anywhere near as much sunlight as they would in orbit, maybe not even as much as they would on Earth or Mars
Actually no :) The light levels at acceptable flight altitudes (~51-55km) are comparable to Earth on a clear day (except that you also have almost as much light also reflecting up at you as coming down at you). Depending on the frequency, it blocks about half of the light from the sun - but twice as much light hits Venus. Mars, however, gets 40% as much light as on Earth - when the dust isn't blowing. Sometimes you get dust storms which can last for months, easily enough to kill plants from lack of sunlight.
Note that solar panels don't have to be outside the envelope, if the envelope is transparent (which I've been assuming thusfar). They can even be built into structural elements (for example, solar roofs on shelters or walkways). It'd cost under 10% of the power, and in turn they'd be shielded from winds, lightning (if a risk), icing (if a risk), corrosion, etc, and your wiring needs would be greatly reduced. I really don't see a point to having anything outside the envelope except for the return rocket (even that's not 100% necessary, but probably a lot easier than a rocket-sized drop-bay ;).
If the ambient pressure is ~1atm, then you have roughly as much air above you as you would on Earth, but without a magnetosphere you're going to be counting on that air to block a lot more radiation.
I read a paper about this before but can't be bothered to dig it up again ;) Okay, okay, just a second.... hmm, this may have been the one. They simulated the Carrington Event and one previous one that was even stronger, and found that even they wouldn't be problematic at 62km (let alone a more realistic 53-54km, which has orders of magnitude more atmosphere over it). That is to say, they calculate 0,09Gy. Radiation therapy in humans is 45-80Gy. A CT scan is 0,008 Gy. So it's like getting a dozen CT scans, but nothing like undergoing radiation therapy. And that's at a much higher altitude than people would actually live at. Long-term GCR at actual colony height, according to their graphs, would be about 1e-8Gy/20h, or 4,4e-6Gy/year - not at all "dangerous". Levels are indeed higher than on Earth, but they're not problematic like they are on Mars. You don't need added shielding, you're sitting under a mass of shielding equivalent to a ~5 meter tall column of water. And the atmosphere above you creates a small induced magnetic field to boot.