First, are you talking about your coop or your run? Using "ground cover" and "coop" in the same sentence is throwing off my understanding of your question.
I use sand in my 4x8 foot coop. It works well if you are someone who is willing to scoop daily. Not so well if you prefer to set-it-and-forget it for several days. (crushed limestone construction sand from my local gravel company)
I use straw in my 10x20 foot run. sorry. my run is roofed with wire, but open to the elements. I find the straw gets worked down into the soil by the hens and breaks down into a rich beautiful loam over time. The loam drains nicely, as opposed to my native clay soil which barely drains at all. I occasionally throw some aspen shavings in the worst spots if it's an especially muddy area.
Best wishes on your change-over, whatever you decide on .