[@Azkott] they both do that but some say Phrik alloy is stronger as it even survived the destruction of a planet hit by the death star. But some sources depict Cortosis to short circuit the lightsabers upon making contact with it. Like deactivate the opponents lightsaber for a couple of minutes. 

If you accept this mechanic I'll go with Cortosis, otherwise I'll be choosing Phrik. No need to waste your time on research.