I rewrote and deleted several things trying to talk about leaves in coop vs run. I have a space in a shed with an open side that functions as coop and run. So, I don't have experience with a typical run. In concept, I think a mixture of materials would work best - especially with a variety of...
Leaves are absorbent enough for a coop if there are enough of them and enough ventilation. Having enough is beneficial in other ways too. Particularly, enough sq ft is good for flock dynamics, enough depth is good for resilient flooring when they land from the roost and other raised areas...