Basically the richer the variety of different strains the better. I would look for products that have different bifido and lactobacilli strains, especially lactobacillus rhamnosus and lactobacillus reuterii. 😊 And I would always choose the stronger probiotic - the children's probiotic tend to be quite light weight and bigger proportions are in most of the cases safe to take. Best taken with an empty stomach morning and evening, or if the dose cannot be shared, whenever the stomach is empty. Changing the brand (even with the same strains) every once in a while is recommended since not all brands are as effective. What brand gives the best outcome depends on the person's own microbiome, so it varies from person to person.