From a physical perspective, the whole concept of lighter scopes being more recoil proof is actually a bit of a fallacy. What damages things is acceleration. For a given amount and direction of recoil force, a lighter scope accelerates more and a heavier scope accelerates less. Heavier scopes have more inertia, which means that they are harder to accelerate. But that also means that they put more strain on the mounting system than a lighter scope. So heavier scopes are harder on mounting systems, but are more resistant to damage from recoil. Of course this assumes that a large part of the weight increase is in the tube and not lenses or other parts that also stress connection points and fastening methods within the scope. A simple analogy would be comparing the damage done by the acceleration of a child versus a large man when an identical force is applied (like a body check). The child would go flying across the room, while the large man might stumble back a little.
In terms of the most recoil-proof scope, I agree with JCM that most of the design features he mentioned would increase resistance to deformation and damage, and would add to the list the feature of having a small ocular and objective housing. By positioning the mass of the scope closer to the center of the scope tube, there is less torque applied on the tube. So with no way to qualify this, I would guess that the NF ATACR 1-8x is probably one of, if not the most recoil-proof scope on the market.
