A note about my weapon of choice: Yes, I like Bic ball point pens. They’re cheap, you can find them anywhere, they don’t run or bleed on the page, and they feel the most to me like a pencil. Except I don’t really like using pencils anymore (for a variety of reasons, but most of all because I want to commit to my marks and don’t want to waste time erasing). My time at Gnomon heavily influenced my to decision to sketch with pens.
The Bic allows me to sketch very lightly, which is a huge plus, but decent darkness can also be achieved. If I need even more contrast, I will go over my Bic lines with a Pilot G-Tech C4. I was introduced to these by watching Scott Robertson. They’re excellent pens. If I’m sketching traditionally, these 2 pens are what I end up using about 90% of the time.