For instance - on a High Speed Velo we actually use very little wing. They are very flat, and are positioned for very little downforce and drag. But the speeds are in excess of 55 MPH so a little downforce lip can produce a ton, compared to a LARGE wing on a small SHORT TRACK running 25 mph.
There are alot of things that go into picking a wing, width of the wing, size of the sides, and the kickup.
More kickup the more drag and down force, the larger the sides the more side force you will get in the corners to help the car from spinning and staying planted to the track. And the width of the wing also helps with down force the wider the more down force you will have. How and where you mount it makes a big deal also, pod mounted, body mounted, high, low, etc...
Not an expert, but this is what I have learned. Some of the more experienced drivers may have more technical info. Hope that helps