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 fan-favourite sequel with harder levels and deeper secrets.

Execution · Practiced Mastery
The most demanding of the New Super Mario line, with brutal optional challenges.
Donkey Kong Country 2: Diddy's Kong Quest leans Execution (Practiced Mastery); New Super Mario Bros. U 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.
Donkey Kong Country 2: Diddy's Kong Quest
Demanding jump chains and animal-buddy control
New Super Mario Bros. U
Challenge modes demand tight, precise platforming
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Donkey Kong Country 2: Diddy's Kong Quest
Fixed enemy patterns, no adaptation
New Super Mario Bros. U
All enemy behavior is scripted
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Donkey Kong Country 2: Diddy's Kong Quest
Secret Lost World entrances hidden until found
New Super Mario Bros. U
Deterministic level layouts
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Donkey Kong Country 2: Diddy's Kong Quest
Routes, DK coins, and bonuses fully mappable
New Super Mario Bros. U
Routing star coins and secret world shortcuts
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.