The left HK was made entirely with polymer clay, middle is cold porcelain and the right is resin. It's pretty clear that the cold porcelain shrinks when it dries. That's a bit of a problem, though I still like how easy it is to use and keep clean. As I mentioned previously, I try to shy away from white polymer clay and I had tried to use red clay for the bow but it bled and ended up looking pretty terrible. So I think in a pinch when size doesn't matter too much, I'll use the cold procelain. When I have time, I'll definitely use resin. I haven't tried painting it yet because I need to put another layer of resin on top to give it more of a shine, but I have put some paint on another piece (below) and it looks like it'll work just fine.
The left is resin and the right is polymer clay. I had made cold porcelain My Melody but put it in a resin piece for testing. Same problem as the HKs. I'll stick with cold porcelain or resin in the future.
It's pretty clear I'm having a love affair with resin right now. There's still PLENTY of reason to use polymer clay (anything that can't be put into a mold), but for my molds I'm turning more and more to resin. Resin has two strikes against it: cost and time. In comparison to clay (maybe an hour to create, fire and glaze...depending on the item), it takes an eternity (at least two days). Cold porcelain is great for solid color pieces (you have to add paint to color it) but it shrinks when it dries and dries relatively quickly (though takes a day or so to cure completely).