Which of the ordinary dungeons in Dungeons & Fighters is the most difficult?

In Dungeon and Fighter, which one is the most difficult among ordinary dungeons? You can refer to the following:

In Dungeons and Fighters, Heroic Nightmare is the most difficult among ordinary dungeons.

Taking the DNF110 white map copy as an example, Heroic Nightmare requires players to reach 33989 reputation points before they can challenge it.