A successful forced landing is when everyone gets to walk away unhurt. The condition of the aircraft when the it comes to a safe stop is utterly irrelevant, therefore the condition of the landing surface is the least important consideration when conducting a forced landing.
A steady 9 Gee de-acceleration from 60 knots to stopped requires a run of about 25 feet. Now obviously there is little practical application for this interesting fact but it does go to show that once the aircraft is on the ground and slowing down at a steady rate you are pretty much home free. The killer accidents are the sudden stop, either as a result of hitting an obstacle while still airborne or hitting a solid immovable object like a stone wall or deep ditch on the landing roll.
When I teach the forced approach I place the majority of the emphasis on picking a field which is easily reachable, without any drastic manoevering, and has a clear approach. As long as the field is reasonably level without any significant immovable obstructions it is going to be good enough.
I have seen a lot paralysis by analysis from students as they tried to pick the field, which resulted in a botched result, as a result of too much emphasis being placed on field surface condition by their instructors
In any case the accident record shows that approximately 80 % of all engine failures are directly caused by the actions or inactions of the pilot, with fuel starvation/mismanagement/contamination and carb icing dis-proportionally represented. All are 100 % pilot preventable and so I think as a general comment flying schools should place more emphasis on not having the engine fail in the first place over complicated strategies to pick the best field after the engine stops.