The Pit certainly stands out as an exemplar for designing a challenging quest; similarly, Tear of Dhakaan stands out as an examplar for an overall dungeon design. Both rate 5 of 5 in my book, and are the best quests under Level 10.
As for jumping, I am having great difficulty mastering the very last jump in The Newcomers. But I'm proud to say that I have managed to "touch the sky" in the Price of Freedom.