Hi Amanda, Straw is a long used, very traditional bedding steeped in history. Having said that, many things improve with time and new technology and I think this is the case with horse bedding.
There are many reasons farms choose to use straw, most often because a farm may either grow their own or get a great price on straw in their area.
Straw is not good when it comes to absorption, ammonia control, cleaning efficiency or disposal volume. There has to be a substantial monetary motivation from my perspective to continue to use straw.
Pine is the single most effective substrate for animal use and with the advancements in producing a pine bedding that is no longer just a sawmill by product - it is difficult to find anything better than pine.
From there, you'll look at the options within the pine category to select a product that best suits your requirements.
If breeding, you may want a fine product at the base for super absorbency and a traditional flake on top close to the muzzle.
To reduce consumption, disposal and stall cleaning time - you'll probably select a pine pellet or mini flake.
For a combination of volume and easier picking, a small flake may make most sense.
With all of the options within the pine category - I am confident you'll find a perfect bedding using pine.