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.

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

Optimization · Pure Optimization
A physics puzzle game about building wobbly towers and bridges from living goo balls.
Portal leans Optimization (Pure Optimization); World of Goo leans Optimization (Pure Optimization).
Portal leans a little harder on execution, though the gap is small.
Portal
Portal placement timing modest.
World of Goo
Placing goo balls needs only mild precision
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Portal
No adversary modeling player.
World of Goo
No opponent exists
World of Goo leans a little harder on variance, though the gap is small.
Portal
Deterministic chambers; no randomness.
World of Goo
Physics are visible and deterministic
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.
World of Goo
Tower structure and goo economy are solvable per level
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.