I have Spotone, Dyene (both made by Retouch Methods --now deceased), and the retouch materials made by Veronica Cass (supposedly retiring). For retouching a dust spot on a negative a red material (coceine (sp?) scarlet or something of that color is usually more effective. Red does not give as hard an edge to the retouched region as black. Especially if one can dilute the red down. Having all of those materials...for dust spots I am usually more inclined to go with a fine point red Sharpie pen.
The advantage of Cociene Scarlet or the Dyene Red is that it can be diluted and applied with a very fine 4/0 brush.
A lot depends on how much the negative is enlarged. For contact printing it doesn't require as much precision as for a greatly enlarged negative.