Unpainted for me.
After the sculpting and moulding costs have been spent out, I suspect that the actual material costs for producing a metal figure won't be that much greater than a plastic figure (I'm sure one of the dealers / manufacturers will correct me if I'm wrong. The greater expense has surely got to be in the hand painting of the figures.
If the idea is to provide a cheaper alternative to the 'standard' (sorry, that does kind of underestate the quality) metal painted figures, then surely unpainted has to be the way to go.
Besides, painted metal will primarily be aimed at adult collectors for display purposes. Plastic could be for the younger (and quite probably more 'mature' collector to play with.
I wouldn't let my kids play with any of my painted metal, but do, occasionally and reluctantly let them play with unpainted plastic.
My two pennys worth.
Simon