I agree that button boxes on the steering wheel and the look in general are not so important in VR, but the shape and dimensions of the rim are important, no matter if you can see it or not.
There are round rims in different diameters, which are perfect for road cars and rally cars. Road cars rims are usually 38 or 35 cm, which is also common in old rally cars, although these normally use deep dish rims. Maybe that's too big for sim racing, especially if you own a weak motor (non-direct drive). Modern rally cars normally have 32 or 33 cm rims. Some GT cars also use small round rims. Old F1 cars also have very small round rims (30 or 28 cm), as well as some lightweight cars such as the Caterhams, etc.
The next step is D type wheels, which have a flat bottom. That's good for cockpits that do not have much room, so the steering wheel doesn't interfere when entering or exiting. This kind of rim is usually seen in some GT cars and especially in road sports cars and supercars.
A mixture of D wheels and round wheels happens when we flatten also the top of the rim, which prevents the top of the rim from blocking the view of the road, which is more important in cars with a very low seat position, such as GT cars. A clear example is the Sparco P310.
For more extreme and circuit oriented cars such as GT cars there's a tendency to use rectangular rims, or whatever they are called. I mean the kind of rims which are only grabbed on the sides, with a fixed position for your hands. There are many varieties of this kind of rims, with horns on the top or the bottom, very lightweight and small such as DTM rims, or more bulky. This kind of rims need cars with low turning degree, since you are supposed to never release the rim from the fixed position. F1 cars use this kind of rims, normally more crowded with buttons and controls and with integrated screens. Of course these rims must have paddle shifters moving with the wheel.
Apart from all this, consider also the tipe of grip of the rim, which can be round or oval. Also, there are different type of materials: pvc. leather, suede, alcantara... Suede and alcantara are prefered for racing, because they provide better grip, but always use gloves if you want them to last. As regard the material of the structure of the rim, the best is carbon fiber, because it's strong and lightweight, but very very expensive. And alternative is aluminium.
