Without question, the hardest golf shot in the world is a wedge off of a hard dirt surface.
It’s the hardest golf shot because an 8th inch fat or thin, and you send the ball a country mile!
It's also a hard golf shot because you must accelerate aggressively into the ball on your down-stroke.
Creating high backspin is hard to do, as backspin is created by high club head speed, a scarey thing when you are only 10 yards off of the green!
Another issue that makes this the hardest shot in golf is the “bounce” that you get on a 60 degree sand wedge:
In some cases, it's not as hard to use a 54 degree gap wedge without bounce so that you can successfully "chop under" the ball to create the high backspin.
For complete tips on striking the hardest shot in golf, see the book Puzzle Duck Golf by Brad Clayton: