What is better to use if you're making clothes;- a typical dressmakers dummy or an adjustoform one?

The adjustable ones would be my choice every time. Not everyone has a body that's the average shape and an adjustable one will reproduce how you are, so unless shop clothes are always a perfect fit you will find one that reproduces your personal shape better. And if you change shape you can reshape it instead of having to buy a new one. I had a wire one that you actually put on and had someone squash it to a skin tight fit. (My husband did it for me and got a bit over excited, but that's another story...