So much depends on how well you're playing and hitting the ding, at least it does for me anyway.
On some courses, BPB for instance, I can have a pretty off ding day and still score reasonably well. At Oakmont or Merion the same standard of play would end in a cricket score.
Assuming I'm fairly well on form my ranking from hardest to easiest, ignoring the Best of and TruGolf courses, would be:
Olympic
Merion, pretty much a tie for 1st though
Pinehurst
Kiawah
Congressional
Oakmont
Royal St. Georges
St. Andrews
Bethpage
I place Kiawah fairly high because the greens are so unpredictable, if you're hitting very close that's not a problem but if I take my average of 12 feet then they can be very tricky.
As I mentioned at the start though, any of them can play easy and the next round they turn into a monster.
Personally I really like that about WGT, I think it's how it should be.