Fresh would undoubtedly be better. How do you cook yours? I plan to saute some garlic and onion, and then add the cuitlacoche (even though the cans already include some onion too).

I read that usually epazote is added, but I don't have any. In fact, I found this page with a whole bunch of herbs I'm not familiar with and am now curious about:
http://www.foodsubs.com/HerbsHisp.html

(edited to fix typo)