I have (not) deep (enough) litter (mostly), rapidly becoming dirt in the original run. It was clay-y sands, or sandy-clays, so "dirt" is an improvement. The new run is still green. That, too, is rapidly changing.
There isn't one universal "best" choice, you need to take into account your climate, drainage, specific run set up (roofed, unroofed), maintenance routine, budget and availability of materials.