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

Optimization · Practiced Mastery
A PSP-born GTA prequel adding a business empire system to 1984 Vice City.

Optimization · Practiced Mastery
An open-world action game where hacking the city's infrastructure is your main weapon.
Grand Theft Auto: Vice City Stories leans Optimization (Practiced Mastery); Watch Dogs leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto: Vice City Stories
Driving, aiming, and helicopter handling on a stick
Watch Dogs
Cover shooting and driving at modest difficulty
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto: Vice City Stories
Mission enemies are scripted and predictable
Watch Dogs
Online invasions add a small human element
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto: Vice City Stories
Mostly fixed missions with light traffic randomness
Watch Dogs
Guard placements are knowable on approach
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto: Vice City Stories
Empire-building business system layers economy onto missions
Watch Dogs
Hacking chains and camera routes make stealth solvable
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.