Well I've got one for most challenging: Pasatiempo.
#1 - 457 downhill, call it a par 5, call it a par 4, I make more 6s than 4s either way. Trees are thinned on each side from what they once were (thankfully) but it still takes a very precise tee shot and approach to get on or close to that green. Then if you miss it, no chips are easy. It also slams you hard right away with an example of the Mackenzie greens you will face - lots of contour both obvious and subtle.
#2 - 437 par 4, also downhill, fairway looks massively wide and is, but it cants pretty hard to the left so left rough and bunkers are a more likely spot than it seems. Turbo-boost rolls on right lure many over there, but trees and worse await a shot too far right. Still, the hole seems relatively benign and definitely plays shorter than the yardage... but then one gets to the green. If there was a definition of "killer green" this would be the picture. NO shots are easy on or around it - severe contour sees to that.
#3 - 235 very uphill with death right, awkward hill short, just requires a perfect wood for most of us.
End result is I can't remember a round where I stood on 4 tee less than +3 - it's usually worse. And I am not very good for sure, but I am also not alone in this. Good players also struggle with these holes, or at least I think so....
But most challenging does not necessarily equal BEST. For best, I think it would be important to have a mix. But then again three great par 4s would work too.
As for which architect brings it straight from the first tee, hmmm... it's not typically a Mackenzie thing, but he had Pasa #1 as a treeless par five, so he doesn't count. How about Tillinghast? Winged Foot West sure smacks you the first three holes....
TH