I hate hay (I have never had access to straw, but I would think it would respond similarly). the hay acts as a solid surface where the poop just sits and stares at you! Wood chips seem to suck up the poop and are easy to mix up and make the poop disappear.
I LOVE sand. It makes poop disappear almost as well as the sweet PDZ and helps drain all the water, and doesn't mold. so YEAH!
My problems with sand:
the rodents tunnel right through it with ease (but then, what do rodents not get into?)
I can't think of any other negatives
As to it being cold....my chickens don't sleep on the sand.
I installed poop trays for the first time this summer, and I am now an almost fanatical convert. Why?
1. the Sweet PDZ almost completely eliminates odor
2. it is super easy to clean
3. the rest of the coop stays spotless (compared to how it was before the poop tray, it isn't *really* spotless)
4.the poop tray makes the perch area much less drafty and much warmer
5. the poop tray pretty much adds a bunch of extra square feet, which is perfect to help combat cannibalism and other winter nasties
In years past I have used wood shavings (aren't they free in most of Alaska?????) in my 8x8 coop, and the attached chicken shed has always been sand.
The wood shavings absorb the moisture in the air and become a solid lump of immovable ice. (I think I am too close to the coast
)
The sand becomes pretty solid too, but never seems quite as bad.
Now, a pile of wood chips or leaves of something, tossed in a usually un-pooped area for them to play in and alleviate winter boredom, priceless!
I right now have sand everywhere, even in the 8x8 coop (main sleeping area) and I think I might stay with sand there over the winter, but I might switch to wood chips, since they will now be protected from the majority of poops, and are fun to play in. Dunno yet.