Of the courses I've played, I'd say the Irish course at Whistling Straits has...a great first 15 holes...the last three (or at least two) you can have.
Oh, wait, that's a different thread (best opening 15)...my mistake. Take two...
After the Walker Cup, it would be difficult for me to deny Merion's rightful place.
From personal experience, I did like 16-18 at Tobacco Road, although I liked 14 better than 17 and 15 better than 16, so I can't place it ahead of Merion.
I agree with Mac that the final troika at PDGC is great, but it doesn't have a quarry!
I'm going to present a Walter Travis Canadian trio that has been incredibly improved by one Ian Andrew. The 16th at Cherry Hill is a pitch of 130 yards to a mini-volcano green. Ian mastefully expanded the front bunker to be a mini-Hell bunker, much more menacing than before. The green is small, but has a bowl in front and a top shelf in back. #17 was a ho-hum, straightaway par 4 of 390 yards (or 6000 meters, if my metrics are correct...) that Ian revamped by adding a back left tee...the hole now plays about 435 from back there but, more importantly, is a left to right dogleg. Add the right fairway bunker arrangement to the hole and you now have a demanding drive that before was an afterthought. The 18th really needs no mention, as it plays about 520 or 580, depending on your tee, to quite possible the most difficult green that Al MacKenzie didn't design. The closing par five turns and climbs gently from right to left. You can get home in two, but you might still make 7.