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

Execution · Practiced Mastery
The NES classic that introduced Kirby's copy abilities across a colourful, secret-stuffed Dream Land.

Execution · Practiced Mastery
A coin-obsessed 2D Mario built around hoarding a million coins.
Kirby's Adventure leans Execution (Practiced Mastery); New Super Mario Bros. 2 leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Kirby's Adventure
Easy platforming with optional tougher secrets
New Super Mario Bros. 2
Standard 2D Mario jumping precision
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Kirby's Adventure
Scripted enemies and bosses only
New Super Mario Bros. 2
Fully scripted enemies
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Kirby's Adventure
Hidden switches found once, known forever
New Super Mario Bros. 2
Fixed levels, known secrets
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Kirby's Adventure
Copy ability choice and secret routes
New Super Mario Bros. 2
Coin-rush routing for maximum collection
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.