Aspen for everyone except breeding tubs. Don't want to risk aspen on hemipenes. I remember when I started breeding a bunch of losers were trying to belittle me when I asked if this was an issue by asking me if I have zippers on my pants. I think everyone should have an opinion, but that wasn't necessary. Now that guys like justin k posted on youtube about it many use paper for breeding. Maybe the guys on that particular forum are used to breeding their wives on the dirt ridden matresses in their trailer parks. Oh, and I used paper towels during mite treatment and quarantine etc., also damp paper towel for hatchlings before first shed.
I recently tried corrugated wrap paper instead of newspaper in breeding tubs, and it seems more absorbent so I don't wake up in the morning to find the bigger snakes swimming in pee.