I use the dimple and sand method wherein you don't necessarily pierce the shimstock with the needle, but raise a "pimple" and sand it using fine (400 or 600 grit), wet-or-dry sand paper. I sand wet with a gentle circular motion. I think my most recent pinhole, made for WPPD last April, was my best yet. It may have been helped by using 1 mil brass shimstock instead of my usual 2 mil. The thinner stuff is a bit harder to keep flat and not damage it, but since the ideal pinhole has a knife edge, the thin stock gets closer to the ideal automatically. Roundness, and an absolute minimum of edge upsets - tears, etc. is necessary for really good results. This year's pinhole camera was a 4x5, it does seem that larger formats produce sharper images.
I used a .014 inch (0.36 mm) pinhole for a body cap adapter for my Bronica SQ-A (poor man's Hasselblad! )a few years back. The pinhole to film distance was about 90 mm.