head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto: San Andreas demands more optimization; Need for Speed: World demands more execution.

Optimization · Practiced Mastery
A sprawling open-world crime epic with RPG-style character stats across a whole state.

Execution · Practiced Mastery
MMO street racing testing driving lines plus grindable car-build advantage.
Grand Theft Auto: San Andreas leans Optimization (Practiced Mastery); Need for Speed: World leans Execution (Practiced Mastery).
Need for Speed: World leans clearly harder on execution.
Grand Theft Auto: San Andreas
Flying school and drive-bys need decent hands
Need for Speed: World
Racing lines, drift control and pursuit evasion reward clean hands
Need for Speed: World leans clearly harder on reads.
Grand Theft Auto: San Andreas
Gang AI is scripted, never adaptive
Need for Speed: World
Human rivals in lobbies add slight positional prediction
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto: San Andreas
Territory wars and traffic add light randomness
Need for Speed: World
Pursuit spawns and lobby skill add mild noise
Grand Theft Auto: San Andreas leans clearly harder on optimization.
Grand Theft Auto: San Andreas
Stats, gym, weapon skill, and routes reward systematic play
Need for Speed: World
Car builds, powerups and route knowledge compound advantage
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.