head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; Transport Tycoon Deluxe demands more variance.

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

Optimization · Pure Optimization
The definitive transport network sim where perfect rail signaling and routing is the whole game.
Portal leans Optimization (Pure Optimization); Transport Tycoon Deluxe leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Transport Tycoon Deluxe
Pausable map clicking, no 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.
Transport Tycoon Deluxe
AI competitors follow simple mappable logic
Transport Tycoon Deluxe leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Transport Tycoon Deluxe
Industry placement and economy events add slight noise
Transport Tycoon Deluxe leans clearly harder on optimization.
Portal
Pure puzzle-solving optimization.
Transport Tycoon Deluxe
Signal logic and network throughput are literally an engineering problem
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.