I prefer the Aspen and currently use ZooMed from PetSmart (we got this as the adopted BP we got was on pine!), cheap, easy, and seems to hold humidity well as we are at a constant 52% in his temp glass enclosure.
He also seems to "enjoy" it as well
There are others as well, and posts will be coming...
Desert Snow is made by T-Rex. It's made from hardwood pulp (think fluffy paper) and is very absorbent and pure white so it's easy to spot clean. It's also nearly dust free, which is important to me because I worry about RI's. One big draw back is that the stuff in not cheap...matter of fact, it's prolly the most expensive substrate out there, but I don't have a large collection, so works for me right now.