In this piece, I experimented with a range of tips and tones of Sharpies.  I had a huge tip, and Ultra, and a Fine in black and than a metallic sliver and several grays.  I really like Sharpies because of their clean look.  There is not much layering and shading has to be done with a sort of cross-hatching or the gray makers.  I suppose if you had a blending pen with some solvent, you could do more.  I really like the blackness of the black and the distinct edges.