in reply to My handwriting implement of choice is…
Pilot G-TEC-C4 (see e.g. net stores.)
I've been using these for at least a decade. They aren't expensive, but break easily. I buy a dozen at a time, so I'll always have a few around.
The winning feature is that you can write with really small details. (Ads claim 0.2 millimeters line widths, iirc.)