Declaring one variant universally harder ignores rating systems, personal strengths, and puzzle craftsmanship. Killer Sudoku stacks arithmetic atop Sudoku geometry—extra cognitive load—but diabolical classic puzzles may demand deeper fish nests than arithmetic shortcuts solve. Challenge comparisons must specify publisher tiers and solver profiles.
Where Killer spikes difficulty
Sparse cages with wide tuples force sustained combination tracking alongside Sudoku scanning—taxing for players uncomfortable juggling sums.
Where classic Sudoku spikes instead
Minimal givens plus hostile fish configurations may resist Killer-style shortcuts entirely.
Personal aptitude matters
Arithmetic-confident solvers may find Killer smoother than opaque classical grids; pattern savants inverse.
Measuring challenge responsibly
Track solve times across matched difficulties rather than vibes.
Also log cognitive strain: did your eyes fatigue from scanning faint cage lines? Did arithmetic interruptions spike heart rate? Subjective load explains mismatches where clocks suggest parity but experience diverges.
Scenario snapshots
Consider a newspaper Killer packed with narrow two-cell cages—likely faster for arithmetic-confident solvers than a sparse classic Sudoku demanding swordfish chains. Reverse the scenario when Killer cages sprawl across boxes while classic puzzles remain singles-heavy.
Competitive rounds alternate variants intentionally because organizers know fatigue profiles differ; hobbyists can mimic that rotation to stay adaptable.
Teaching contexts
Students anxious about math sometimes perceive Killer as harder despite neutral ratings—introduce mini grids first (see 4×4 Killers) before judging innate difficulty.
Further comparison reading
See how Killer differs and easy vs hard Killer.