What is the optimum f-stop for a pinhole?

I looking for an opinion on what is the best pinhole f-stop.

I have a f-stop of ~356 or F16-10. Would a larger aperture be better? This is about a, if I remember correctly, about a 8 0r 16 second exposure on a bright sunny day. 100ASA film.

The picture I got is soft but acceptable for a contact print. I have not seen a lot of pinhole print other then in magazines so I have noting to compare it to.