I've used sawdust but now get free fine wood shavings/sawdust mixed (which I prefer) at a small local sawmill. We just take large garbage bags and a shovel. Doesn't take long to fill a dozen bags. When we used them for animal bedding we'd fill the pickup but it's easier to not have to tarp it to keep it from blowing away. We've had it hauled in but the trucking charges are high. The big sawmills may not give it away as they ship it for industrial purposes. The small mill is happy to get rid of it and a lot of the small hobby farmers are happy to have it. Sawdust takes almost forever to break down by itself. There are huge decades old piles back in the bush here where there were small sawmills and they are still recognizable as sawdust. Depending on the wood species it will turn grey (probably cedar) but the fir/spruce/pine stuff we get stays new looking for years. I mix it with compost, grass clippings, and alfalfa tea and let it sit awhile for mulch. Becomes a nice brown color and breaks down almost completely in a year in the perennial beds. I wouldn't use ground pallets altho we do use them whole as compost bins. Hope there's no leaching of chemicals.

I agree with The Virginian. I'm trying to replace some of my lawn with shrubs and flowers, so whenever I need a new area cleared, I lay down cardboard, then whatever organic material I can get my hands on. One of my neighbors gives me his grass clippings, so that usually goes on first. Last fall, I collected 30 bags of leaves one afternoon, and shredded that, then laid it down over the grass clippings. I've been having a ball all spring, watching various kinds of birds pick through it, looking for bugs. Besides eliminating the need to cut off the sod, by the time I plant an area, the top few inches is actual soil. (Under that, unfortunately, is pure, heavy, clay.) Shredded leaves, raked out evenly, look just as nice as mulch, IMHO.

Oftentimes, the pallets are made from pressure treated lumber, which is known to contain toxic products.

It's not really a question of which is most nutritious as which has nutrients that are more readily available and those are in leaves. If one looks at what Ma Nature does we would find that she uses a combination of leaves and wood to maintain nutrient leaves where she is in charge. The slugs appeared because you created an environment, cool and moist, that they like with that leaf mulch so yes the leaf mulch could be why the slugs appeared. However, they would have appeared if you used straw or anything else that would have created a cool, moist environment. kimmq is kimmsr