Change Baby Milk

Hi mummies, i need help. My baby 6M having diarrhoea so doc recommends me to change to Lactose Free (Enfamil) for 1 week. After 1 week doc say can change back to old milk (Lactogen Stage 1) but incase baby still diarrhoea need to change to other brand. Im not to sure to change to Nan Optipro or S26 Gold Any recommendations please help thank you. And what the difference between Nan Optipro and Nan Supermepro H.A