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 · Pure Mechanics
Trilogy capstone whose equal-start arena multiplayer defined a console generation.

Execution · Competitive PvP
Stick-skill basketball execution layered with predicting a human opponent's play-calling.
Halo 3 leans Execution (Pure Mechanics); NBA 2K10 leans Execution (Competitive PvP).
Halo 3 leans a little harder on execution, though the gap is small.
Halo 3
Precision aim and grenade-melee timing
NBA 2K10
Shot timing, dribble moves and defense need real stick skill
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Halo 3
Equal-start fights reward predicting humans
NBA 2K10
Human opponents' play-calling and tendencies must be predicted
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Halo 3
Equipment pickups and spawn variation
NBA 2K10
Shot RNG and bounces add modest game-to-game noise
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Halo 3
Power-weapon timers and map control
NBA 2K10
Roster knowledge, play-calling and matchup exploitation reward study
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.