Using wood shavings of various types.
Tried indented kraft paper and it was hit or miss. It seemed many animals could not get "comfortable" on it. With larger colubrids that make a lot of waste, they would cruise through the puddles and get streaked with crap. It was a mess.
Dried pine (mallard creek mini micro flake) and Harlan Tekklad aspen is what I alternate between, depending on what the local feed store has in stock. I keep a shop vac in the snake house so the mess is negligible. When the snakes crap or pee, I vacuum up the spot and it's surrounds, clean it with F10sc and place back a scoop of new aspen/pine. Simpler than paper and the snakes - as a whole - seem to prefer it.