So I've already read this link, and a few other similar ones, and the main issues I am already aware of... but yet it still seems like a large majority of the designs for rotating (for 'gravity') ships and stations use a torus, or perhaps a cylinder.
Why is this?
The main issue I have, is the radiation shielding. It seems that if you're using water (for example), you would need 2 tonnes of water for every square meter of surface area. So if you use a torus, that's a huge amount of extra weight. A sphere is (by a fair margin) a shape with a better volume/surface area ratio. And saving those 2 tonnes per square meter would make your fuel consumption significantly better.
Is there something I'm missing? I suspect there is. In my head a torus just seemed like a much more 'streamlined' shape (not aerodynamically, just much less waste of volume). But it seems like the sphere gives you much more volume for much less mass, mostly due to the shielding requirements?