Personally, I prefer metal sheet or foil flags, painted.
Metal sheet or foil looks more in-scale than most cast metal flags (like the flag King-White used for its Napoleonic Prussian flagbearer). Though, I would not pass up a resin flag, in suitable scale thickness and properly draped.
Printed cloth or paper flags just never look right to me. They usually look out of place with the style in which the figure is painted.
Prost!
Brad