I don't have them, but I have a buddy that has 90 colubrids and many, many prized king snakes among them. He uses cypress and swears by it. He got me to try it and I love it for my pythons as well. Good absorption, humidity, etc. (it may be a bit too wet right out of the bag, so air-dry it first if it is.)
I use cocohusk. It's ok I had to put a few air holes in my tubs though cause it was getting my humidity to high. I like it keeps everything smelling nice. Snakes like it they eat me out of house and home on it.
I know plenty of people use it with great success. I just don't personally care for it. I've used it in the past, tried new things and eventually found I prefer a blend of Eco-Earth and Repti-Bark. Aspen tends to mold easier than other substrates, plus I like the look of the other substrates better. The Eco-Earth still allows them to burrow while maintaining humidity, while the Repti-Bark provides a good look as well as good humidity control.
It really comes down to what you prefer and what works best for you and you animal. Geographics and climates can also play a role in what works best for you and you animal. I change my ratio a bit seasonally to help make humidity control easier on myself, too.