head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; The Bluecoats: North vs. South demands more variance.

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

Optimization · Pure Optimization
A turn-based tactical strategy game set in the American Civil War.
Portal leans Optimization (Pure Optimization); The Bluecoats: North vs. South leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
The Bluecoats: North vs. South
turn-based tactical inputs, minimal reflex
The Bluecoats: North vs. South leans a little harder on reads, though the gap is small.
Portal
No adversary modeling player.
The Bluecoats: North vs. South
scripted AI in campaign, not adaptive
The Bluecoats: North vs. South leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
The Bluecoats: North vs. South
random battle resolution elements
Portal leans clearly harder on optimization.
Portal
Pure puzzle-solving optimization.
The Bluecoats: North vs. South
tactical unit and formation optimization
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.