It's up to you. A lot of people use aspen and a lot of people use newspaper or kraft paper or a combination of both.
~~McKinsey~~
"Men have forgotten this truth," said the fox. "But you must not forget it. You become responsible, forever, for what you have tamed."
~The Little Prince; Antoine de Saint Exupery
I really liked Desert Snow when I used it. Its main drawback was that it was expensive compared to the alternatives out there. I do remember another thread where someone called it something else and said they were buying in bulk, can't recall what thread but it was a picture thread. Its a white substrate that made spot cleaning very easy; you always knew when something was soiled and it clumped well.
Edit: Heres an old picture of my tank set up with the substrate.
~*Rich
1.0 100% Het Albino
1.3 Normal
1.0 Spider
0.1 Mojave
1.0 Pastel 100% Het Goldfinger
0.1 Pastel 66% Het Goldfinger
0.1 Pastel PH Goldfinger
"Men have forgotten this truth," said the fox. "But you must not forget it. You become responsible, forever, for what you have tamed."
~The Little Prince; Antoine de Saint Exupery