The correct answer is
Rise of the Runelords. Why? Because these people wrote it, while being guided by James Jacobs, who is the best architect/developer of adventures in the RPG business:
James Jacobs, Richard Pett, Nicolas Logue, Wolfgang Baur, Stephen S. Greer, Greg A. Vaughan. You can
maybe quibble about Stephen Greer in the HoF and replace him with Tim Hitchcock for your 6 Hall of Famers, but there are lots who will say "keep him in".
That's why
RotRL is the best. You can run it in 3.5, PF1, or convert it to PF2 or 5e (it's pretty easy to convert this; really go try it!). It's still the best AP overall where the authors were each doing their DAMNDEST to save Paizo as a company -- what they thought of as "saving the spirit of Dungeon Magazine" at the time. They pulled out all the stops and it shows.
And save it they did, too. The thing about
RotRL which sets it off from other APs so clearly is that "the back nine" is as strong "as the front nine" -- THAT is why it is the best.
Typically, APs tend to be really good in the first 3 volumes( or half), and tail off significantly in the second half.
Kingmaker suffers from this. Kingmaker is
spectacular in Vols 1-3, but the back nine... it tails off too much in quality and pacing; it often feels like a different adventure entirely. The BBEG in Vol 6, in particular, was not telegraphed properly and essentially comes out of nowhere. The re-written Kingmaker for PF2/5e addresses this - or tries to. The back nine is still perceptibly weak in
Kingmaker though.
The inconsistency in the 2 Dungeon APs (
Shackled City doesn't even count as a true AP as it was written with a very different method) is the reason neither qualifies as coming even close to the podium overall. They are all over the place in quality, and all have "disappointing back nines" in terms of quality. The main reason for this is that WotC interfered with Paizo's design decisions on the Dungeon APs and refused to let Paizo make significant story awards for XP points to escape the grind, such that each of these APs are grindy AF.
I do love
The Whispering Cairn and think it is one of the best 3.5 module released considered on its own (
Red Hand of Doom is almost as good and a far longer module though which maybe presents more of a challenge?) Still, by the time you get to Chapter 8?
AoW goes off the rails and descends in to ceaseless hack and slash. ( I have run
AoW twice - once under 3.5 and the other under PF1). I only ran Savage Tide once - that was more than enough, thanks.
Nothing for PF2 has stood out yet to the same degree. Vol 1 of
Abomination Vaults, by James Jacobs of course, is outstanding and a call back to what our altered perception (distorted by nostalgia) likes to think 1st ed was at its best. (In truth, 1st ed dungeon crawls was never as good as AV1 is). The problem is that Vol 2 of this 3 volume AP is weak and needs work to make it a worthy sequel to the excellent Vol 1. It's fixable, but really, I shouldn't have to do that.
1st Ed - It's
DragonLance DL1-14 and it's
not even close. It was the first true AP, though some of the things it did we have decided to not do again. That doesn't change the fact that much of what it did changed adventures and adventure writing
forever. There is a reason we keep talking about this damned module series, nearly 40 years later.
2nd Ed - Weak edition in the epic adventure department. I think people were still mainly running 1st ed modules at the time, tbh.
Night Below and
Rod of Seven Parts I guess would be the nominees but those are both ..
iffy long format adventures,
at best.
3rd -
Rise of the Runelords
PF1 -
Rise of the Runelords Anniv Ed. Curse of the Crimson Throne Anniv Ed comes close though -- Why? Once again, it also has a "strong back nine".
5e - Likely
Curse of Strahd. You might go with
Rime of the Frostmaiden, but both of these require far too much DM prep work and alteration to work properly out of the box. WotC can't be bothered to finish the adventure design job properly and release adventures where the DM
plainly has to do WAY too much work to call it a finished product. Note: Paizo does not do this --
not even a little bit. It is a significant difference in the quality of the adventure products published by the two companies.
PF2 -
Abomination Vaults or
Kingmaker, until the inevitable
RotRL Rev Ed for PF2 is released, that is. Or just play the unofficial PF2 conversion:
GitHub - A-Series-of-Dice-Based-Events/RiseOfTheRunelords: A repository to hold tools for those wishing to run and convert RotR to Pathfinder 2E.)
Not yet mentioned -- but deserves to be? Chaosium's
Masks of Nyarlothotep. It's a lot of fun, too. Still, it is very incomplete as initially released and thus the
MON Companion is necessary to fix it and bring the whole thing together to present a more coherent whole.