I'm with
@aart and
@ChickenCanoe on this. The best material for your run is cheap, readily available, and requires limited maintenance on your part.
Plenty of people are willing to set up and scrape poop boards, rake sand, and the like in the hen house. But even a modest flock benefits from a good sized run. Raking that is a LOT of effort.
Straw, leaf litter, wood chips all have the benefit of controlling odor and decomposing slowly, improving the soil and helping to raise the run level - which helps ensure rain runs "elsewhere". If you have enough run that your chickens don't totally destroy your ground cover, green growing things are great - but at that point, your "run" is probably better described as "pasture" (this is what I do).
Others use coarse sand, because they can't establish a viable, durable, "green", and leaf litter/chips/straw are impractical (of the three, straw can mat down, which can be a problem). I have had terrible experience w/ sand (and also gravel) but that's specific to clay soils, high rainfall rates (54" per year, average), and ducks.