Good Question...
For me when I first started to play back in the Stone Age....lol.... St.Andrews was the easiest ... now that is one of the hardest for me.. off the Blacks, it's a tough course.
Back then too, Beth was the Hardest... it was a nightmare to play.... Now I think it's the Easiest
I luv playing Cabo.... Whistler is not good... and I don't play it Oak, Kia Cong...are all good.
Oly... can't putt on those greens...lol.. so I avoid it if I have to.
Merion is interesting..... maybe easy but can bite you big time.
Rsg can be great depending on conditions.... not that bad though.
Like any course.... if you play em often enough as previously said they can be ok depending how your shooting at the time.
Beth for me for easiest
-Roger