Dungeon had a circulation that seemed to vary in the 30-60k range and relative to the numbers of D&D players it never had the impact of say Keep on the Borderlands and each issue had multiple adventures so standing out from the crowd is probably harder.
So in this thread I am going to go through the magazine starting at issue 1 and picking the best adventure IMHO that stands out and is the most interesting to run. This is a bit flawed as I have not played all of the adventures but if I have I will mention it.
I can also do requests as well so if you want to pick an issue suggest it and I will see what I can do. IDK if that is a great idea but I'll see how it goes. Several names that are still around now also crop up in the pages of Dungeon- Wolfgang Bauer, Erik Mona and Mike Mearls come to mind.
In 1986 First Edition was the D&D of choice while BECMI was still around. Work on 2E had not yet started AFAIK (that was 1987 IIRC) Issue 1 has 1 D&D adventures in it with 5 AD&D adventures. Its probably not to hard to figure out whats popular. Of the 6 adventures you notice one stands out. Into the Fire eats up 19 pages out of 64, the rest of the adventures are quite small. Its also the best one and the Boucher brothers who authored it turn up in future issues. The adventure is my pick for the best one not due to its length although it perhaps helps but because its also interesting with an outdoors overland hike to get to the dungeon. It also has a somewhat decent plot hook.
The basic gist of it is a group of nights decided to confront Flame a red dragon and they all perish with one exception. One escapes with a necklace from the Dragons horde. The survivor dies and the necklace is sent to the King who recognizes that it belongs to his missing son who died at sea (guess what destroyed the boat).
So a bit of travel, exploration, a mission for a king all tied back to the Dragons lair. Not a bad effort at an intro and tying things together with a touch of mystery. Like any good villain Flame also returns in a future issue.