I've used the Sani-chips and shredded aspen. I'm using shredded aspen now(I also switch to newspaper on occasion).
Sani-chips tend to just get everywhere, and be messy, get into the water more, and overall had no real positives over the shredded aspen.
Shredded aspen was much easier to find and cheaper(I buy mine in big blocks at Tractor Supply) and although it tends to scatter a little if I'm in too much of a hurry, it's not as bad as the sani-chips. It's easier to spot clean to me too, since if a spot gets wet, it's a smaller spot than the sani-chips.
I guess sani-chips would be safer if your snake ate a few bits as the tiny bits would pass through the digestion without any issue. Otherwise, I don't see much difference other than personal preferance.