As such there is no cement called good or bad cement. Blended cements (PPC & PSC) are superior to OPC as they have better technical benefits for improved durability.
Amongst blended cements, PSC is superior to PPC. Chemical composition of Slag and Fly ash differs. Chemical composition of Slag is almost similar to that of cement where as in case of Flyash does not contain lime. Hence Slag cement (PSC) helps in getting better and uniform properties in concrete in comparison to Flyash (PPC) cement.