Originally Posted by jur

I'm the odd one out here on wheel size:

I find there is an insignificant difference in the feel of the bike wrt wheel size, when speaking of road bumpiness. I have a narrow-tyred 451mm wheeled bike, a wider-tyred 406mm-wheeled bike (Moulton with suspension) and a Brompton. I don't think the Brompton gives the harshest ride; I think long elements like the seatpost dominates whee size; and riding habits dominate that again. For the latter over the years I have aquired the habit of always lifting a bit off the saddle when going over bumps, even just tensioning the legs up will make a huge difference compared to lead-arsing it over bumps. IMHO that is the primary effect.

The Moulton with its suspension is definitely the most comfortable. The harshest is the 451mm Ti Swift. But even that bike I ride from time to time on MTB-suited terrain, ie mixed dirt audax rides, and while a MTB is surely more comfortable, technique is king.
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So based on my own experience, I don't hesitate to recommend a 16" bike for firm dirt. But if you are going to negotiate loose surface tracks where wheels may sink a little, that is definitely going to be worst choice.