Condottiere said:A variant of Skeletal Warriors.
An efficient automated killing machine wouldn't be bipedal.
Depends. The Terminators we know from the movies were mainly infiltrator units so those things need to be able to blend in. Then there is the fact that making them humanoid allows them to use weapons and machines that are meant for humanoids. (And to fit in buildings and vehicles as well if you need to do boarding or urban combat.)
You could have drone-tanks, drone-fighters and other kinds of robots (smaller recon droids?) but there are plausible reasons to make approximately human sized and shaped robots if you plan to use them to fight with or against humans.