head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is execution, and it is a single point.

Execution · Twitch Chaos
A casual slide racer testing little beyond steering and shortcut knowledge.

Execution · Practiced Mastery
A grittier crime story where weighty driving and gunplay carry the experience.
Aquapark.io leans Execution (Twitch Chaos); Grand Theft Auto IV leans Execution (Practiced Mastery).
Grand Theft Auto IV leans a little harder on execution, though the gap is small.
Aquapark.io
Steering and shortcut jumps need only light touch
Grand Theft Auto IV
Heavier driving and cover shooting reward control.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Aquapark.io
Opponents are mostly bots; nothing meaningfully adapts
Grand Theft Auto IV
Scripted AI, no adaptive opponent modeling.
Aquapark.io leans a little harder on variance, though the gap is small.
Aquapark.io
Bumps and crowding add slapstick randomness
Grand Theft Auto IV
Minor mission variance.
Grand Theft Auto IV leans a little harder on optimization, though the gap is small.
Aquapark.io
Knowing shortcut launch points is the thin strategy layer
Grand Theft Auto IV
Mission routing and weapon picks learnable.
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.