Ballpoint pens are my favourite tool. Once I discovered how easily varied pressure could, in turn, vary the resulting lightness of the line, I was all over it - it didn't smudge like pencil once it was dry, after all, and biro black and biro colours would always have identical behaviour. Equally, it made for a great challenge - erasing lines you already drew was no option, after all - and so it quickly became my standard.

Of course, the medium's biggest problem is blotching - and part of the reason I've stopped actively drawing nearly every day is because I no longer have any ballpoint pens that are of a sufficiently high quality as that it wouldn't be a constant issue.