When creating character designs often sketch concepts in 2D, however I also use 3D-Coat to create rapid voxel sketches which I feel give a better overall impression of the design. PBR vertex painting makes it easy and fast to create variations of designs and texture concepts, which can translate quickly into a final game asset.
Images show a selection of sculpts with vert/poly painted colour, spec with shader based normals. Rendered in 3D-Coat and Marmoset.