I use both, normally. when I do veins like in leaves, or feathers, like in bird wings, I will first cut them with a small straight blade then go back over them with a small spiral.. great way to easily in crease the kerf, just enough that it shows better. but not too wide. And like I said in another post, I I shave to thicvkness things like grass blades, whiskers, small twigs with them. A Flying Dutchman 3/0 or a Pegas 2/0 is great for this.