head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; Secrets of the Ark: A Broken Sword Game demands more variance.

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

Optimization · Pure Optimization
Tests deductive puzzle-solving through fixed adventure-game logic chains.
Portal leans Optimization (Pure Optimization); Secrets of the Ark: A Broken Sword Game leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Secrets of the Ark: A Broken Sword Game
Point-and-click input with generous action timers
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.
Secrets of the Ark: A Broken Sword Game
No opponent of any kind to predict
Secrets of the Ark: A Broken Sword Game leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Secrets of the Ark: A Broken Sword Game
Puzzle solutions are hidden information until discovered
Portal leans clearly harder on optimization.
Portal
Pure puzzle-solving optimization.
Secrets of the Ark: A Broken Sword Game
Every puzzle has one fixed solvable answer
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.