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

Execution · Practiced Mastery
Licensed bike riding and building that asks little beyond basic handling.

Execution · Practiced Mastery
A grittier crime story where weighty driving and gunplay carry the experience.
American Chopper leans Execution (Practiced Mastery); Grand Theft Auto IV 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.
American Chopper
Bike handling on missions is the only real demand
Grand Theft Auto IV
Heavier driving and cover shooting reward control.
Grand Theft Auto IV leans a little harder on reads, though the gap is small.
American Chopper
AI riders follow fixed lines
Grand Theft Auto IV
Scripted AI, no adaptive opponent modeling.
Grand Theft Auto IV leans a little harder on variance, though the gap is small.
American Chopper
Courses and missions are scripted
Grand Theft Auto IV
Minor mission variance.
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
American Chopper
Chopper part choices matter, but shallowly
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.