It would be good to have a list of the cleaner burning woods. I'll guess hickory, hedge, and locust are some of the cleaner burning ones. Ash would be dirtier in my opinion. I judge how much a wood might contribute to creosote based on the flames it produces. Hickory and hedge don't produce much fire, while sappy pine and Ash do. The fire is flammable vapor burning from the resins inside the wood. Sure you can close the e air vents to reduce the flames, but the resins are still getting baked out, and are not burning, so they condense on cooler surfaces. Give the fire more air to burn clean, and it will burn too hot. So, I just burn hot occasionally, so the heat and extra air help evaporate and burn off deposits in the stove pipe before there's enough to cause a problem. That is one advantage of having a stove pipe: you can burn them hot reasonably safely.