I would think without question the hardest type of hole to design well would be the very long par 4--the 450-490 yd type hole.
For the moment it's just too much to talk about this type hole from the perspective of every single type of players. For that tees need to be set well.
I'm talking about very long par 4s from the perspective of say low handicappers who hit the ball a wide variety of distances. Some really long par 4s just aren't designed to accomodate good players who aren't particularly long. The reason is generally they just don't have options for the shorter hitting good players that are particularly sane in their risk. Generally the available option for the shorter hitter in this type hole might require him to hit about his absolute career best distance-wise to be even remotely safe. And that type of option generally shuts the option down so it really isn't tried--never a good thing for a design option!
When that kind of thing happens design-wise you generally find the shorter hitter just laying up with some lofted club. That's not really what I consider great multi-optional design. There should be something in the design of these very long par 4s that would TEMPT a shorter player to try something different, maybe also somewhat risky but imaginative that did not depend completely on almost career best raw distance to be successful.
Some holes I'm familiar with that are not at all accomodating of a shorter hitting low handicapper.
Huntingdon Valley's #7! The first creek may be a bit too far to carry for a good amount of good players and particularly into the wind. What that player is left with then is hitting less than a driver off the tee and then being left with no options other than to lay up in the next landing areas before the next creek and then play another 9 iron to the green. I think there should be something else somewhere design-wise and strategically to allow that golfer to do more than that. So a hole like that falls short in the spectrum of its design, in my opinion.
#18 Applebrook and #14 Moselem Springs from the tips have margins for error with their approach shots for the shorter hitter that are too slim to be used enough I think. So does #17 Inniscrone! There are so many more like this!
A hole like Merion's #5 at its new yardage of 470, I believe, can actually work well for either a long hitter or shorter hitter although the options for each are very different. It's possible for a shorter hitter to get on this long par 4 though, just in a very different way. He'd probably do it best by carrying the ball with a fairway wood over the bunker short of the green on the right and caroming the ball onto the green.
The longer hitter with a more lofted iron actually has to carry the ball well past the front of the green or his ball will filter left hard and backwards off the green in front (I didn't realize until the other day how amazing this latter design ramification really is).
But because of the great topogaphy to the right of this hole a shorter hitter could carry the ball maybe up to 35-40yds less than the stronger player on the approach and actually come out much better. I think this is extremely interesting and indicates a excellent hole with multiple and diverse options although it does happen to be a very long par 4.
It sounds to me like a few back nine long par 4s at Rustic Canyon might have some of this wide spectrum of shot options and distance requirements but if pulled off properly gives the shorter hitter a chance to do even better than the strong player. Then of course there was that great 72nd hole 4 wood by Pavin at Shinnecock bouncing the ball in. The design of the hole gave him that but he had to hit a good one--but it didn't require so much of him that he didn't try that option--a great hole!
I say for a very long par 4, possibly the hardest hole of all to design and design well, those very diverse options that can result in the same reward as the stronger player who might play them entirely differently shows real design quality!
And there is one other thing that can highlight those interesting and diverse options on really long par 4s and make them play even better!
"The Ideal maintenance meld"!!