The difference will just be the time it takes for them to grow into adults and breed. 1/4" mealworms will take ~2 months to become adults, while the larger mealworms will take less time. Which size you get will only matter for the first generation since they are all the same kind of mealworm, just a different ages. Does that make sense?People offer different sizes of mealworm like 1/4 in, 1/2 in, and 1 in. I was wondering which size is best?