Brompton is 16" and so is Bike Friday pakiT. Comparing apples to apples, having ridden both, no hinge is always going to be stiffer than a hinge frame. Now expanding to 20" wheelers, my Dahon Mu Uno has a center hinge and I think it is stiffer than the offset hinge on Brompton.
Ride quality is 20">16" (assuming both bikes are of similar quality), no hinge>hinge. Other factors like long stems may affect handling as well. Being a fairly short person who doesn't like sitting totally upright, I've not had any issue with that.