After having tried all of then I think that Natures Best is the best, far more absorbant. I now use that on all 16 of my livery horses. One bag per horse per week and they have good deep, dry beds.
I moved from Woody pet to Natures best as I found the pellet size on the woody pet was getting smaller every year and as such it was becoming less absorbent. Also the price of the Woody pet had gone up quite significantly and as I was buying 2 pallet loads every time it was quite a difference. I pay approx £4.60 for a bag of the Natures best. If I buy 3 pallet loads I will get it at about £4.40.
I've used aquamax for 4 years and i love it for my horse. It's really absorbant, doesn't smell, dust free, quick to muck out, can't be eaten and i only use one bag per week (£5.95 each). Haven't used the others but i would recommend any bedding like this for horses with respiratory problems, allergies to straw or wet horses. I have converted 4 other people to it!!