Well, based on my (somewhat scanty from a quantitative point of view, but definitely intense and fun...) experience, a ballpen is the single most excruciating device to play with a nyloned footsie! But use it nicely, delicately, and intermittently... A feather quill also works miracles (or tortures, depending from the point of view...), but it may scratch nylons and get stuck, so it's cumbersome to use with those...
In my opinion, fingertips and nails are the best: why would you ever lose contact with the skin of your beloved one?? Hands are more personal, more intimate, and you control them in many more ways, because they are just your hands! 😀
But then, just my two cents there...
Cheers all!
justadinosaur...