head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Optimization · Pure Optimization
A hidden-object mystery about searching scenes and solving puzzles to crack a case.

Optimization · Pure Optimization
Noir DS adventure about interrogating hotel guests to unpick a mystery.
9 Clues: The Secret of Serpent Creek leans Optimization (Pure Optimization); Hotel Dusk: Room 215 leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
9 Clues: The Secret of Serpent Creek
Clicking hidden objects needs only patience
Hotel Dusk: Room 215
Stylus puzzles need negligible dexterity
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
9 Clues: The Secret of Serpent Creek
No adaptive opponent in a casual mystery
Hotel Dusk: Room 215
Characters follow a fixed narrative script
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
9 Clues: The Secret of Serpent Creek
Object and clue locations hidden until found
Hotel Dusk: Room 215
Story info hidden until questioned out
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
9 Clues: The Secret of Serpent Creek
Working through puzzles and deductions is the loop
Hotel Dusk: Room 215
Choosing right dialogue and solving set puzzles
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.