​The National Association of State Foresters has published an article debating whether to stack firewood bark up or bark down. They concluded that there are benefits and drawbacks to both ways. When storing wood under shelter, it would depend on personal preference and ease of handling. When split wood is stored outdoors bark down, it is possible that water can collect in the u-shaped trough, causing prolonged drying and accelerating decay. When storing the split wood bark up, it was questioned whether the bark would protect wood from long-term photo-degradation, but it wouldn’t degrade the wood enough to significantly affect thermal output. It was suggested that smaller logs be put perpendicular under stacks of wood to allow for better air-flow and reduce the chance of infestation.

Resources
Wood for Home Heating, The Education Store
Insects in Firewood, The Education Store
Firewood Rules, Indiana DNR
Heating with Firewood, Indiana DNR

National Association of State Foresters