Paulo, use the hard setting only for track. Its not quite safe to do fast cornerings on bad roads with too hard suspension, but i guess you already know that.
You cant say wich setting is best, each car is different.
The best policy is to adjust it at medium settings. You have to experiment a bit.
Try to adjust your suspension having the following behaviour.
The suspension must move up and down with ease, but not too easy. A good test is to pass over various bumps and notice if the car moves up and down more that once. If this happens, you have to stiffen it a bit.
Follow this. Adjust it to the softest. You will notice that the car on bumps hops up and down more that once. It does two or three oscillations after passing the bump. Harden it a bit. Do the same test. Harden the suspension till the second oscillation barely starts.
Remember, your suspension must KEEP its absorving capability. This is for safety. But, it must not be too soft to allow more than one oscillation.
My english is not good, i hope you got my point
Hope this helps