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

Execution · Pure Mechanics
The hardest NES Castlevania, with branching routes and switchable partner characters.

Execution · Pure Mechanics
Capcom's infamously punishing arcade platformer that makes you beat it twice for the real ending.
Castlevania III: Dracula's Curse leans Execution (Pure Mechanics); Ghosts 'n Goblins leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania III: Dracula's Curse
Brutal platforming and tight whip timing throughout
Ghosts 'n Goblins
Committed jumps and pixel-precise throws, no mercy
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania III: Dracula's Curse
Scripted enemies and bosses only
Ghosts 'n Goblins
Enemy spawns are scripted
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania III: Dracula's Curse
Minor enemy spawn wobble
Ghosts 'n Goblins
Red Arremer movement adds slight noise
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Castlevania III: Dracula's Curse
Partner choice, route branching, pattern memory
Ghosts 'n Goblins
Weapon choice and route memorisation are mandatory
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.