I keep a selection of pens for drawing. I often use a Uni Pin fine line pen 0.4 (which is waterproof), a Pentel brush pen and a fountain pen. I also, just like to use a biro. I think it's not really the pen as much, as just drawing.
If you are worried about mistakes, do a quick, light pencil drawing first. Otherwise, don't worry, just leave in your mistakes and work over them.