Dennis
As an avid Benchrest Competitor, most would naturally assume I would say, "Of course, 100-200 yard Benchrest". But, I am not so niave as to think that.
I have stated it many times on these Forums, every shooting Discipline has some unique quirk that produces the level of difficulty. There are many shooting Disciplines that require a certain amount of athletic ability. (man, does that leave most of us out). This could involve eye hand coordination, stamina, and quickness. Heck, I might be able to get down into the prone position, but getting up is the problem.
Others involve a strong mental capacity, being able to think at a moments notice, and make correct decisions based on what what you observe.
Others are very equipment oriented. Of course, paramount in this field is Benchrest, whether it be 100-200 group, score, or long range. The finest shooter on the Planet cannot overcome the deficiencies of a Rifle that is not up to the task. As for 100-200 yard Benchrest, it all starts with the Rifle. The simple fact is, great Rifles make good shooters. That is why most of us spend so much time insuring that the Rifle is up to the task at hand.
But, which is really the most difficult test of marksmanship for most Humans to master?? Anything that involves off hand shooting, such as many Pistol Disiplines, and Rifle Disciplines such as High Power.
The simple fact is, the shooters that participate in those types of shooting could learn to do what I do. But, I doubt very seriously that I could master what they do, for obvious reasons. Mybe 30 years ago, but not now.......jackie