There's no real good answer to that from what I can figure. Just as long as you aren't using something harmful, like pine or other such woods then you're good to go. Some are more expensive than others and some look better than others. From what I can see, aspen and newspaper are very very widely used, but they look like crap (IMHO). Repti-Bark and Forest Floor look great, but are expensive. Poo is easy to find in Aspen and Newspaper, but not easy to find in Repti-Bark and Forest Floor. There is one big advantage to Repti-Bark and that is that it is re-useable. You can clean the stuff. Kind of a pain but it does look great. I'm a very asthetic person and I love to use repti-bark, but aspen is way easier and that's what I'm using right now.
So to answer your question... yes it is fine, expensive and not very practical, but it looks great and is safe.