This year I started every hatchling out on ASF hoppers..they move around way more than rat pups and that really seems to be the difference. I can say that every snake I started on the hoppers typically took their first meal the first time they were offered it. they get 2-3 hoppers then right to rats..out of the 30 some odd babys I did this way this year not one of them had any trouble starting or switching to rats.
I have a few stubborn feeders that just pound ASF's so that's what they get fed..big ole adult ASF's. I don't how ever like to feed established juvi's or adults ASF's cause I have heard and even had one get stuck on them..once they start on rats I try to offer nothing else, only as a last resort would I offer ASF's to an established Rat eater.