Which pencil should I use for shading?

Generally, the B is good for medium to light shading, and the 2 B for medium to dark, and you should be able to get a good range of tone (value) out of both, from quite light through to dark. Try them both, on a piece of scrap paper, to see which suits you best. Many artists like to use one of these mid-range pencils for pretty much everything, controlling lightness and darkness by shading more or less heavily. However, sometimes you might want a bit more intensity, or find that you can't get your midrange pencil to go light enough or dark enough.
The 4B is good for darker shading. It is soft enough to give a good layer of graphite quickly, without blunting too fast. The 6B pencil is good for very dark areas, but is very soft and blunts quickly, so is difficult to use for detail. Because it blunts so quickly, It tends to look grainy, skimming over the surface of the paper. When burnishes - shaded very, very heavily - graphite can look very shiny. Harder pencils contain more clay, so look a little less shiny than a very soft pencil.
The harder grades of pencil - from HB, through H, 2H to 5H - get progressively harder, easier to keep sharp, but also grayer and less shiny, because they have more clay in them. The harder pencils can dent the paper very easily. The HB and H can be used for fine, light, even shading.
Layering pencils - try shading an area with a hard pencil to flatten and smooth the grain before shading with a soft pencil. Shade over an area of soft pencil with a hard pencil, to smooth and even out the graphite, and create a more even surface appearance between the different types of pencil.





-Drawsketch