Right now she's on newspaper because she had mites but it's not very pleasing to the eye. :0)
If you have one snakes with mites, all your snakes will probably get them. You should put all your snakes on a simpler substrate and treat all your cages with Provent-a-mite. If you simply treat one cage, the problem will come back in a few weeks and you will be constantly battling it.
As for the substrate preferences....
Pine is not a good idea. There is some evidence that the oils can lead to respiratory problems in both rodents and reptiles.
Bark is OK, but it is hard to tell when it is dirty and therefore your cages are never likely to be as clean.
Aspen shavings are the best in my experience.
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Chris Harrison
...he was beginning to realize he was the creature of a god that appreciated the discomfort of his worshippers - W. Somerset Maugham