head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; We Were Here Together demands more variance.

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

Optimization · Pure Optimization
A two-player co-op escape adventure built on describing what only you can see over voice chat.
Portal leans Optimization (Pure Optimization); We Were Here Together leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
We Were Here Together
Walking and interacting; minimal physical demand.
We Were Here Together leans a little harder on reads, though the gap is small.
Portal
No adversary modeling player.
We Were Here Together
Partner is an ally; puzzles never adapt.
We Were Here Together leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
We Were Here Together
Asymmetric hidden information is the core mechanic.
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.
We Were Here Together
Fixed symbol-and-mechanism puzzles, fully solvable once both sides known.
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.