I like Kaytee Aspen and I've never had a bag that was dusty, not even towards the bottom.
That's the brand I have too, but so far most of the bags I've opened have been dusty. Even the stuff that's been in the tank now for a month, when I spot clean the puckey, it kicks up a little bit of dust. Maybe it's the manufacturer for this part of the U.S., I don't know.
Shredded aspen is the best for corn snakes!
What about the coconut fiber substrate? We bought a few bricks when we bought our corn. She seems to really like it and we can see her sooo good in it. (She's amel.) She burrows way down in it and will stick her little head out. It's so cute.
i had been using aspen shavings, but when i went to the vet, he strongly suggested against using that or sand, etc, b/c of the possibility of snakes ingesting it, which can be fatal. I don't know if it's as serious as he puts it, but I'm switching to reptile carpet, as he had suggested, just to be safe. Just make sure not to feed them in the cage where all the substrate is!!