This is an old pic so not the quality I normally would post but we did this one on a campout. I think it was apple wood. I personally prefer oak. I don't soak my chips too long, maybe an hour before. I also put them on the grill top above the heat. Especially for pork or chicken.
White oak only, preferably Missouri white oak. I make my own fat coals which is a process of burning white oak hot and liloing the fire out. You get these.
american chestnut. it's pretty much extinct so hardly anybody uses it.....except me....hahaha....it's almost delicate...imparts a mild almost nutty flavor.