I used to make a lot of simple, graphic drawings for screenprinting and scratchboard art (like animals, runners, cyclists, trees, whatever). When sketching for that, I would just use ink pens like a Sharpie or UniBall. This way I can quickly block in shapes and decide where to play the darks and lights off of each other to aid the design. I also like pens because I like to stylize elements and make things really graphic. So it’s not so much about rendering, although I’m changing my attitude about that now.
To work up a sketch I’ll take my ink pens and start drawing on tracing paper. Then I’ll layer another sheet on top and redraw it, changing things here and there. I’ll do this for as long as it takes to get the drawing exactly the way I want it. The problem with layering tracing paper over and over is that sometimes the “soul” of the drawing gets lost. The lines can start to look contrived and predictable and lose energy.
Now that I’m starting to work digitally, I’m finding that it’s easier to retain the freshness. I can do a rough, imperfect ink drawing, scan it in, and alter elements infinitely. Now I’m just erasing and redrawing things like with a pencil, but still have my bold pen marks. It’s the best of both worlds.