Yes, it's all relative (!) but I know the worst hole couldn't possibly be 2,3,4,5,6,7,9,10,13,14,15,16,17,or 18.
That leaves 1,8,11, and 12. Personally, I have always liked 1 and 8 despite what a smart friend notes (the driving area widens at one the farther you hit it and the 8th features a 'catcher's mitt' green).
In my book, that leaves 11 and 12. I really like the diagonal drive at 12 BUT I haven't hit to the new green. The prior one was loaded with character. Comparatively, the blind drive off the 11th tee to a narrow fairway holds little strategic value IMO. Its green is probably the least interesting on the course though some will contend that a flat green causes its own challenges.
So ... if you want to know how good Merion is ... and you want to get a sense of it versus all others ... ask yourself what other course's worst hole would be 11th at Merion.
Impressive.
Best,