Choose by the obstacle
There is no measured hardest-puzzle ranking here. A long recorded input route is not a difficulty score, and a frequently discussed room is not necessarily the one blocking your run. Start with a visible layout feature.
Specific rooms to compare
Two Traders crossing separate islands: compare the long two-Trader Mirror room, then check the starting mirror and exit positions before opening its hints.
Three heroes and six upper plates: compare the room with three upper cells and a broad lower hall. Its complete route coordinates all three abilities.
Four heroes and eight dragons: compare the four corner rooms and the two monster-gated goal chambers. This is a different identification problem from a lone Thief room with four dragons.
When the first match is wrong
Do not transfer a full sequence just because the same hero appears. Compare the number of goals, the initial selected hero and the location of each movable object. If any of those disagree, return to the Finder or record the layout in your notebook.