At various times I have worked my way through bare earth, (mud nightmare) concrete blocks (where does the muck go when you hose them off? It just turns into slurry at the side of the run) autumn leaves (the girls loved them but they got really horrible to clear out after a few weeks) wood chippings (quite good but went mouldy, very bad for your lungs when digging out, and didn't compost very well) rubber chippings (great on well drained base, though difficult to poo pick as its not absorbent and the poos stick to the rubber chips, which won't compost, but got extremely messy even when hosed down after the first year because although most of the poo is soluble, there is some residue from grass etc that gradually builds up into a smelly cake at the base of the chippings and reduces drainage.)
The only thing I found to be extremely effective, in fact indispensable, is a liner of permeable landscape fabric, well pegged down all over the base of the run. Whatever you put on top, the hens can't dig the mud up through the liner, its light, relatively cheap, light amd easy to lay, and very long lasting if you put a good layer of soft stuff on top.(mine has now been down over 3 years and has lasted out the 2 and a half years of rubber chippings before I gave up on them) its soft and warm on their feet, and landlords don't object, Fuzzyfelt!)
One more thing. Last summer I gave up and had a proper roof put on my run and then I put down a deep litter bed of Aubiose, which is shredded hemp stems. This is highly absorbent so it dries out the droppings, the hens love digging it up into great heaps, and so far I've found it's very easy to poo pick as it sort of coats the droppings with bits of shredded hemp. Under the roof it stays dry, and the first lot I put down has lasted with very little topping up, so inexpensive in the long run.
I wouldn't think sand or gravel would be very good, how would you pick up the droppings and what would you do with the resulting buckets of mess as it wouldn't compost? Also, when you came to dig it all out, it would be heavy, smelly and disgusting - I should imagine you'd have to bag it up and take it to the dump, not good in the boot of your car!
So I'd say, go for the membrane base, and roof as much of the run as you can manage (also this is good for predator control, foxes can get over a 6ft high fence but can't ge in through a good roof.But that's just my personal experience of keeping a few hens in a comparatively small(12 sq. metres) run and other people will have different solutions for their own situations.