Voted plastic for the simple reason that I have yet to utterly destroy a model made out of it. yet.
Metal: Space Marine chapter masters, I broke 2 of the 4 weapons. Can't get greenstuff to stay in place (small details like the end of the handle of a sword) so the models look funny.
Finecast: Feels like I'm going to snap it in half if I set it down too hard. Took 3 hours to clear all the excess flak off the model, and that was a dwarf (runesmith with great weapon)
Plastic: if I break it, oh well. Superglue it back together and pretend it's supposed to look like that.