head to head
Neither is simply harder - they are hard in different places. Animal Crossing: New Horizons demands more variance; Portal demands more execution.

Optimization · Pure Optimization
A cozy island life-sim about building a community at your pace.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.
Animal Crossing: New Horizons leans Optimization (Pure Optimization); Portal leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Animal Crossing: New Horizons
Trivial inputs.
Portal
Portal placement timing modest.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Animal Crossing: New Horizons
NPCs are scripted.
Portal
No adversary modeling player.
Animal Crossing: New Horizons leans clearly harder on variance.
Animal Crossing: New Horizons
Daily visitors and fossils randomize.
Portal
Deterministic chambers; no randomness.
Portal leans clearly harder on optimization.
Animal Crossing: New Horizons
Turnips, layout, and time-routing reward planning.
Portal
Pure puzzle-solving optimization.
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.