head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; The Settlers II: 10th Anniversary demands more reads.

Optimization · Pure Optimization
The portal-gun puzzle game whose solutions are everything.

Optimization · Pure Optimization
Optimising road networks and production chains at a settler's pace.
Portal leans Optimization (Pure Optimization); The Settlers II: 10th Anniversary leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
The Settlers II: 10th Anniversary
Slow road-laying needs no dexterity at all
The Settlers II: 10th Anniversary leans clearly harder on reads.
Portal
No adversary modeling player.
The Settlers II: 10th Anniversary
AI opponents expand on predictable scripts
The Settlers II: 10th Anniversary leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
The Settlers II: 10th Anniversary
Map resources are scripted-but-unknown until explored
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
Pure puzzle-solving optimization.
The Settlers II: 10th Anniversary
Road networks and production chains are the entire game
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.