head to head
Neither is simply harder - they are hard in different places. Portal demands more optimization; Vampire: The Masquerade - Redemption demands more variance.

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

Optimization · Pure Optimization
A 2000 action RPG spanning centuries of a crusader-turned-vampire's redemption.
Portal leans Optimization (Pure Optimization); Vampire: The Masquerade - Redemption leans Optimization (Pure Optimization).
Portal leans a little harder on execution, though the gap is small.
Portal
Portal placement timing modest.
Vampire: The Masquerade - Redemption
Click-driven real-time combat needs little dexterity
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.
Vampire: The Masquerade - Redemption
Enemy AI is simple and scripted
Vampire: The Masquerade - Redemption leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Vampire: The Masquerade - Redemption
Loot rolls and unknown dungeons on first pass
Portal leans clearly harder on optimization.
Portal
Pure puzzle-solving optimization.
Vampire: The Masquerade - Redemption
Discipline builds, party gear, and blood economy
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.