head to head
Neither is simply harder - they are hard in different places. Portal demands more execution; Super Sanctum TD demands more variance.

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

Optimization · Pure Optimization
A tower-defense game about building optimal mazes and tower combinations.
Portal leans Optimization (Pure Optimization); Super Sanctum TD leans Optimization (Pure Optimization).
Portal leans clearly harder on execution.
Portal
Portal placement timing modest.
Super Sanctum TD
Placing towers needs no twitch; abilities are light
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.
Super Sanctum TD
Enemy waves are scripted, not adaptive minds
Super Sanctum TD leans clearly harder on variance.
Portal
Deterministic chambers; no randomness.
Super Sanctum TD
Wave composition is predictable once learned
Super Sanctum TD leans a little harder on optimization, though the gap is small.
Portal
Pure puzzle-solving optimization.
Super Sanctum TD
Maze design and tower synergy are the entire game
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.