I've used Aspen, is nice and clean, but it takes some time to clean up when you have to. Un-printed Newspaper is what I use because it's easy and cheap.

Cypress I have used and did not like it at all. It will get dry and when it gets dry it gets dusty and splinty. I didn't like that at all. Sani Chips I haven't tried, but heard very good things about it, of course it is way more expensive.