Materials What's the best sculpting clay for...

I'm in the midst of making an avian (nonhuman, but still fully-jointed) bjd, and am wondering what the best brand of clay is if I want it as strong as possible and relatively easy to use. I have some Super Sculpey, but what is a better thing to use? (I sculpt for fun, but sculpey does tend to break rather easily if handled too much, and I fear that the slightest movement will upset it).

So what's the best sculpting clay?