I voted for Ruby Passage as it has the most consistently strong set of levels. The Fiery Cavern is probably a highlight for many, me included, but the other levels in the Sapphire Passage don't have the strong refining level variation and ingenuity to them. Hotel Horror is neat distraction, but the individual rooms don't offer base level challenges. I really like level design that takes an idea and uses every inch of the level to explore that idea. This is also why I'm not big on the openness of the Topaz Passage.