Course difficulty ratings:
2.5 Merion
2.5 Best of Hardest
2 Congressional
2 Oakmont
2 Olympic
2 Bethpage
2 Best of Par 5
1.5 St Andrew's
1.5 Cabo del Sol
1.5 Whistler
1.5 Best of Famous
1.5 Best of Par 4
1 Kiawah
1 Royal St George's
1 Best of Par 3
There is no way you can convince me Kiawah is the easiest in the game. Nor is Merion anywhere near the hardest.
Assuming championship greens, I'd rank them something like this, hardest to easiest (excluding the Best Of's, since I haven't played them much):
Congressional
Oakmont
Kiawah
Whistler
Olympic
Royal St George's
Bethpage
St Andrew's
Merion
Cabo
Thoughts?