What is a good size rat to feed my snakes?

i have a ball python and a red tail boa. both are the same size they are 6-8 months old. Ive been feeding then 2 frozen Pinkie rats a week each for the past 2 months with no problem. I'm going to reorder more that will keep me stalked for the next couple of months. my question is should i order rat pups? or weanling rats or are they to big? these snakes wont eat mice for some reason so i have to get rats thank you ahead of time