My experience says that walnut tends to be better at cleaning and corn cob is better at producing a brighter shine. But, it really depends more on what you add to the plain media.

I prefer the 20/40 sieve size media in either since it doesn't tend to hang up in the flash hole. I deprime before I tumble, so in my process it just empties quicker from my Lyman auto-flo tumbler.

I have seen lots of pet bedding that is way too large. I know that some folks have great luck using pet bedding media, but those sizes aren't available in the stores around me.